Navajo Sandstone is a geologic formation in the Glen Canyon Group that is spread across the U.S. states of northern Arizona, northwest Colorado, Nevada, and Utah (the unit is not part of a group in Nevada). It is located in the Colorado Plateau province of the United States. This rock formation is particularly prominent in southeastern Utah, where it forms the main attractions of a number of national parks and monuments including Zion National Park, Capitol Reef National Park, the Grand Staircase-Escalante National Monument, and Canyonlands National Park. Navajo sandstone frequently occurs above the Kayenta Formation and Wingate Sandstone (all three formations are in the same group). Together, these three formations can result in immense vertical cliffs of 2000 feet or more. Atop the cliffs, Navajo sandstone often appears as massive rounded domes and bluffs that are generally white in color.
rockhound, minerals, science, geology, rocks
I bumped into Steven and asked him if he would like to talk about the opal fields near his home. He submitted this article and pictures.
Here is the brief history and present day story about Grawin, Glengarry, and Sheepyard Opal Fields.
The Sheepyard opal field is located approximately 75km west of Lightning Ridge, NSW and forms part of a triangle of opal fields consisting of Grawin, Glengarry and Sheepyard
Opal was first discovered at Glengarry in 1905 by Mr Charles Phipp who was working on Morendah Station at the time, but little mining was done there. The Grawin was established in 1908 with the discovery of the opal at “Hammond Hill”. Further discoveries in 1920 at “Richards Hill” put the unofficial village on the map. Since the first discovery of opal in the region, people have come and gone in tides with each new strike, seeking their fortune in search of the rainbow in the rock. At the time mining was done by candle light with a hand pick and the waste was removed by shovel and bucket and wound up by hand with a wooden windlass. In 1928 an opal weighing almost 450g, and the size of a man’s fist was found at Richards Hill and caused a rush of men to this field. The opal was named “The Light of the Worlds” and is still the best known opal from this area. After the Second World War things began to get more mechanical with the electric generator for light and motorised hoisting gear to make the removal of waste quicker and a bit less like slave labour. Then came the electric jackhammer and the amount of dirt that could be removed increased and the bucket was replaced by wheelbarrows and all sort of inventions to make the job better for the miner and in turn caused an increase in the number of people who came to have a go. The next major rush was started on Melbourne Cup Day in 1985 when the Sheepyard Rush was found. The Sheepyard area was named after a stumble on of opal near the fence of the old Sheepyard. By now the piles of dirt were starting to fill the landscape and this lead to the Short Throw self tipping hoist and tip trucks to remove waste. This led to the invention of the rickshaw to wheel waste to the hoist bucket. By the time the 90’s came along a new rush called Carters Rush had started and Blowers (Giant Vacuum Cleaners) were in use as well as underground hydraulic diggers and mini loaders and as many different inventions as there are miners are now being used in search of the thing that all miners, young and old lust after, “The Rainbow in a Rock”
Although mining at Glengarry was also going on for some time it was not until about 1970 when a find of some very good opal was made that Glengarry became the new “Hot Spot.” The Mulga Rush, which began in 2000, is the biggest opal rush since the Coocoran was discovered in the early 1900’s.
The opal fields of Glengarry, Sheepyard, and Grawin. These towns are accessed via the small village of Cumborah. The roadway between Lightning Ridge and Cumborah is now fully bitumen and is bitumen to the Grawin turnoff. This makes it easier to tow the caravan out to the field. (This section is flooded now; you have to take a 30km dirt road detour!) Mining area roads are gravel in reasonable condition and driven at the right speed, are suitable for caravans and the like.
You can also fossick in the gravel pits nearby Comborah. Another 17 km along in a north westerly direction will bring you to the Grawin field. You can fuel up here and also get basic provisions. From here it is another 7 km to the Glengarry field where there is a pub and a golf club. Sheepyard is accessed from Glengarry and is the youngest of the fields.
Glengarry Hilton is the oldest pub on the Opal Fields and can be a great place to grab some lunch or a cold drink after your hard work driving and fossicking. You can grab lunch there from 12to 2pm daily and dinner is from 6 to 8pm every day. There are showers, toilets, and even backpacker accommodation if you are too tired to drive any further. If you manage to catch any yabbies in their dam they will even cook them up for you. There are locally produced arts and crafts for sale opposite. You can go fossicking at the famous Mulga Rush heaps for a day in another world…Noodling on the dumps is an interesting experience and can be rewarding. It’s fair to say that it can be hard work if you make it so, but there’s a lot of dirt between the good stones. The temps in summer can rise to 40 to 50 degrees Celsius. The opal fields of Glengarry, Sheepyard, and Grawin said to be like Lightning Ridge of 70-80 years ago, great opportunities to see opal mining operations and miners’ camps. Meets the locals on the final frontier of high hopes, tall tales and long beards, see the frontier-style opal field life.
The area is adjacent to the Sheepyard Pub available to campers and as tourists/fossickers in the area.
Showers and toilets outside the pub give ready access for those camping. While the toilets are typical of those in the outback areas, the male and female showers are very functional. You need to gather your own wood, which is abundant in the area, and light the chip heater which heats the water very quickly. After the dusty dumps, the shower is much appreciated. The cost for the shower is $2 as the water has to be purchased by the pub owners and transported in, this is a fair price. There is no charge for camping. Of course, being near the pub had other benefits. Mobil phone coverage, satellite TV in the pub and a cold drink if you needed one. You need to supply your own power and gather firewood for a campfire as you would in any other free camp.
The Sheepyard Pub has an active role in the mining community and is a meeting place for the community. A theme that runs within the pub and the community is respect for our ex service men and women. Visited ex service people are invited to sign their names on whiteboards, which are displayed throughout the pub along with armed service and Australian flags. The Memorial Committee along with the Walgett RSL has constructed a War Memorial honouring those serving in all wars.
Grawin General Store, next to the “Club in the Scrub”. The Store has a very good range of groceries and supplies suitable for the mining area and fuel is also available there. The “Club in the Scrub” is an outback pub and is the Golf Club headquarters. The golf course looks quite challenging with its sands crape greens. A toilet is available for camper’s use but for all other items you need to be self sufficient. Mobil telephone contact can made, otherwise a public telephone is available near the store.
Very informative books for rockhounds. Check out her site!
Where do you get your information?
- From hands-on experience with the gems in the US and abroad.
- Directly from dealers and jewelers who specialize in whatever I’m discussing. For example, I’ll interview several opal dealers if I’m writing about opals and I’ll have some of them check the accuracy of my sections on opals.
- From appraisers and gem laboratories. I also have them check what I write.
- From gem and jewelry seminars geared to the trade. Even though I graduated from the GIA (Gemological Institute of America), I must keep abreast of new developments, sources and treatments.
- From consumers and hobbyists. Sometimes they know more than “experts.”
- From gem shows. This is one of the best ways to learn about gem pricing and availability.
Where do you get your photos?
I’ve taken many of the photos myself (those with no photo credits). The others I get from designers, jewelers, photographers and gem dealers. They get free publicity by having their name mentioned and I get free usage of the photos. There is no paid advertising in my books.
Gail considers himself a lapidary “hobbyist”, although his spectrolite gems are as good as any we’ve ever seen… he gets exceptional rough and has a magic touch with the material. Some of Gail’s cabs were published along with our spectrolite jewelry in Renee Newman’s Exotic Gemstones Vol 1. He also cuts beautiful opal:)
…I’ve never met someone with so much knowledge on spectrolite ~ from the perspective of cutting, the history of the material, the differences between spectrolite versus labradorite, etc.
Gail O. Clark –
Gail is a great asset to the rockhound community. Here is his story and works below. Check out his link in the article to see if he is selling any right now-
Like the experience of so many other rockhounds I began with my wife and I carrying home attractive and sometimes unusual rocks as we hiked the scenic mountains of Idaho. Though I had the usual introductory geology courses in university classes the information, while interesting and often fascinating, really wasn’t applicable to hands-on rockhounding. But it helped to develop a greater interest in rocks and what might be done with them.
My initial introduction to this fascinating activity was a collecting trip to the Spencer, Idaho Opal Mines, about a three hour drive from my home. After using a spray bottle and small rock hammer to actually locate, identify and pick up some exquisitely colored opal from the bull dozed hillside, I decided then and there the family budget could likely stand the strain of buying a six-inch trim saw and an accompanying six-inch flat lap from the congenial owners of the Spencer Opal Mines. . Besides, I told my wife that if I ever produced anything of value, she would get first choice. Presently she has lots of pretty stones!
Over time, and during retirement, we joined the local rock club and took part in the club’s field trips. We visited much of central and southern Utah as well as several locations in Idaho and Wyoming and found that the club members were about as nice and helpful to beginners than we could have ever imagined. There truly is something special about rock people. Soon we had accumulations of dinosaur coprolite, petrified wood, fossil fish, geodes, jasper and way too many other specimens to list here.
Little by little, I purchased additional equipment…lots of additional equipment ranging from a larger slab saw and tumblers up to my prized Diamond Pacific Genie. Learning about the two large rock and gem shows in Denver, Colorado and Tucson Arizona, we decided that at least these two splendid shows had to be seen first hand. We have attended both several times. It’s great to leave the Rocky Mountain winter behind and spend some February time in sunny southern Arizona!
Opal continued to be my primary lapidary interest and I spent significant time and money cutting various types of Australian opal, Brazilian opal, Nevada opal, Mexican cantera opal, and even some delightful and costly man-created Gilson opal. About eight years ago I “discovered” spectrolite, the brilliantly colored feldspar that is a cousin to common labradorite. In doing research for an article for Rock & Gem, I found that true spectrolite’s origin is solely the mines in southeastern Finland. Since that time the majority of my lapidary time has been spent with spectrolite, a superb and fascinating stone that I continue to work with. I import all my rough material from Finland and order only the highest quality material the mines provide. It’s costly but very rewarding to cut and polish.
In the latter part of 2008 a new opal discovery was made in the Welo region of northern Ethiopia. I had previously worked with the older, well known chocolate colored southern Ethiopian opal that proved to be a exercise in futility as this brownish material was unstable, cracked for no apparent reason and was extremely disappointing. But I decided to try the new Ethiopian Desert Crystal opal from the Welo region and I was immediately hooked by the beauty and unparalleled fire in this new Welo opal. Since then I have been splitting my lapidary time between spectrolite and Welo opal and continue to enjoy both these unique and gorgeous treasures from the earth.
Once I was firmly involved with lapidary a friend told me that I’d soon have to start selling finished stones to, as he put it, “support your habit”. He was correct. Selling huge numbers of stones is definitely not my all consuming purpose. Instead, I sell a limited number of finished stones of spectrolite and Welo crystal opal on eBay under the name gails_gems . To set up a Web site would probably detract from the personal pleasure and sense of accomplishment of lapidary as well as cutting into my lapidary time so I have chosen not to do this. I do sell a sufficient number of high quality stones to pay for my lapidary interest and can do so at what I have been told are reasonable prices. A Google search on spectrolite and/or Welo crystal opal will lead you to my finished stones. I typically list a few Welo opals and a few spectrolite stones each Sunday morning. Though I certainly do not consider myself an expert I’ll gladly try and answer any email questions about spectrolite and Welo opal.
For many years prior to retirement I was an active amateur astronomer, spending many late nights in the mountains away from city light pollution, observing the wonders of the sky. I used to write articles for Astronomy magazine, as well as Sky & Telescope and other publications. As a book reviewer I was sent the latest astronomy publications and kept up to date on this exciting field. However, the mirrors of my telescopes no longer gather light from the ancient reaches of the universe; instead, they gather dust while much of my spare time now involves the intriguing world of rocks. Hard to say which is most exciting: rocks or the sky. I am glad I have had experiences of both.
(Mr.) Gail O. Clark
Apatite is infrequently used as a gemstone. Transparent stones of clean color have been faceted, and chatoyant specimens have been cabochon cut. Chatoyant stones are known as cat’s-eye apatite, transparent green stones are known as asparagus stone, and blue stones have been called moroxite. Crystals of rutile may have grown in the crystal of apatite so when in the right light, the cut stone displays a cat’s eye effect. Major sources for gem apatite are Brazil, Burma, and Mexico. Other sources include Canada, Czechoslovakia, Germany, India, Madagascar, Mozambique, Norway, South Africa, Spain, Sri Lanka, and the US.
Gemmy Green Apatite Crystals with Calcite on Matrix, Cerro de Mercado Mine, Durango Mexico
The name, ‘apatite’ comes from the Greek word ‘apate’, which means to cheat/deceive. It was called that because it can easily be confused with amblygonite, andalusite, brazilianite, peridot, precious beryl, sphene, topaz or tourmaline.
Operating since 1952, Rose Creek Mine is one of 3 state licensed gem mines in Macon County, North Carolina. Centrally located in Western North Carolina in the heart of the Smoky Mountains, we are near waterfalls, white-water rafting, AT Trail hiking, museums, antique shops, historic train rides and the Cherokee Indian Reservation.
In our Gem Mine you can find Ruby, Sapphire, Garnet, Amethyst, Citrine, Moonstone, Topaz, Smoky Quartz, Rose Quartz, Quartz Crystals and more! All equipment is provided and we help beginners. You dig your own dirt in our mining tunnel and wash the dirt away in our covered flume. Mine rain or shine. Mining is a great field trip for church groups, scout troops, senior citizen groups and others. We have an educational program that will fit your needs. Scouts can work on their geology achievements and badges.
Rose Creek Mine Gift & Rock Shop. We have rubies, sapphires, garnets, emeralds and so much more. We also have special buckets, gem kits, lapidary supplies, jewelry, Opals and a world class collection of minerals. Last new miner accepted at 4pm. Dig your own dirt, first bucket free with admission. Help for beginners, equipment supplied, covered flume line, clean restrooms, covered picnic tables, snacks. Group rates available as is gem dirt to go. Five miles north of Franklin on Hwy 28, left on Bennett before river. 115 Terrace Ridge Dr. For mining info call 828-349-3774.
Gem Mining Rates
- Major Miners (over 8): $6.00 each (includes 1 free bucket)
- Minor Miners (8 & under): $4.00 each (includes 1 free bucket)
- You dig your own bucket of dirt in the mining tunnel.
- All refill buckets are $4.00
- Super Buckets – $40.00
- Mega Buckets – $75.00
- Mini Buckets – $10.00 – $20.00 – you keep the bucket
- Bags of Gem Dirt to Go – $3.00 ea. or 2/$5.00
What to Bring:
Bring ziploc bags or a plastic butter dish to take your stones home in (no glass). Rubber gloves are handy if it’s chilly or you have a nice manicure and a hat and some sunblock if it’s sunny although we have a covered “flume”.
The wooden benches can get hard as the day goes on so you might need a cushion to sit on or old towels work well too and you can use them to wipe your hands. Wear old clothes and tennis shoes or boots and bring a plastic bag to put your muddy shoes in and an extra pair to wear in the car. Bring a picnic lunch, we provide picnic tables to eat out of rain or sun, plan to spend the day! And you will need to bring the camera for those pictures to show friends you played in the mud in North Carolina and found beautiful gem stones.
Silver ( /ˈsɪlvər/) is a metallic chemical element with the chemical symbol Ag (Latin: argentum, from the Indo-European root *arg- for “grey” or “shining”) and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal. The metal occurs naturally in its pure, free form (native silver), as an alloy with gold and other metals, and in minerals such as argentite and chlorargyrite. Most silver is produced as a by-product of copper, gold, lead, and zinc refining.
Silver has long been valued as a precious metal, and it is used to make ornaments, jewelry, high-value tableware, utensils (hence the term silverware), and currency coins. Today, silver metal is also used in electrical contacts and conductors, in mirrors and in catalysis of chemical reactions. Its compounds are used in photographic film and dilute silver nitrate solutions and other silver compounds are used as disinfectants and microbiocides. While many medical antimicrobial uses of silver have been supplanted by antibiotics, further research into clinical potential continues.
Silver is a very ductile and malleable (slightly harder than gold) monovalent coinage metal with a brilliant white metallic luster that can take a high degree of polish. It has the highest electrical conductivity of all metals, even higher than copper, but its greater cost has prevented it from being widely used in place of copper for electrical purposes. Despite this, 13,540 tons were used in the electromagnets used for enriching uranium during World War II (mainly because of the wartime shortage of copper). Another notable exception is in high-end audio cables.
Among metals, pure silver has the highest thermal conductivity (the non-metal diamond and superfluid helium II are higher) and one of the highest optical reflectivity. (Aluminium slightly outdoes silver in parts of the visible spectrum, and silver is a poor reflector of ultraviolet light). Silver also has the lowest contact resistance of any metal. Silver halides are photosensitive and are remarkable for their ability to record a latent image that can later be developed chemically. Silver is stable in pure air and water, but tarnishes when it is exposed to air or water containing ozone or hydrogen sulfide to form a black layer of silver sulfide which can be cleaned off with dilute hydrochloric acid. The most common oxidation state of silver is +1 (for example, silver nitrate: AgNO3); in addition, +2 compounds (for example, silver(II) fluoride: AgF2) and the less common +3 compounds (for example, potassium tetrafluoroargentate: K[AgF4] ) are known.
Naturally occurring silver is composed of two stable isotopes, 107Ag and 109Ag, with 107Ag being the most abundant (51.839% natural abundance). Silver’s isotopes are almost equal in abundance, something which is rare in the periodic table. Silver’s atomic weight is 107.8682(2) g/mol. Twenty-eight radioisotopes have been characterized, the most stable being 105Ag with a half-life of 41.29 days, 111Ag with a half-life of 7.45 days, and 112Ag with a half-life of 3.13 hours. This element has numerous meta states, the most stable being 108mAg (t1/2 = 418 years), 110mAg (t1/2 = 249.79 days) and 106mAg (t1/2 = 8.28 days). All of the remaining radioactive isotopes have half-lives that are less than an hour, and the majority of these have half-lives that are less than 3 minutes.
Isotopes of silver range in relative atomic mass from 93.943 (94Ag) to 126.936 (127Ag); the primary decay mode before the most abundant stable isotope, 107Ag, is electron capture and the primary mode after is beta decay. The primary decay products before 107Ag are palladium (element 46) isotopes, and the primary products after are cadmium (element 48) isotopes.
The palladium isotope 107Pd decays by beta emission to 107Ag with a half-life of 6.5 million years. Iron meteorites are the only objects with a high-enough palladium-to-silver ratio to yield measurable variations in 107Ag abundance. Radiogenic 107Ag was first discovered in the Santa Clara meteorite in 1978. The discoverers suggest that the coalescence and differentiation of iron-cored small planets may have occurred 10 million years after a nucleosynthetic event. 107Pd–107Ag correlations observed in bodies that have clearly been melted since the accretion of the solar system must reflect the presence of unstable nuclides in the early solar system.
The Lake Superior agate is a type of agate stained by iron and found on the shores of Lake Superior. Its wide distribution and iron-rich bands of color reflect the gemstone’s geologic history in Minnesota. In 1969 the Lake Superior agate was designated by the Minnesota Legislature as the official state gemstone.
The Lake Superior agate was selected because the agate reflects many aspects of Minnesota. It was formed during lava eruptions that occurred in Minnesota about a billion years ago. The stone’s predominant red color comes from iron, a major Minnesota industrial mineral found extensively throughout the Iron Range region. Finally, the Lake Superior agate can be found in many regions of Minnesota as it was distributed by glacial movement across Minnesota 10,000 to 15,000 years ago.
More than a billion years ago, the North American continent began to split apart along plate boundaries. Molten magma upwelled into iron-rich lava flows throughout the Midcontinent Rift System, including what is now the Minnesota Iron Range region. These flows are now exposed along the north and south shores of Lake Superior. The tectonic forces that attempted to pull the continent apart, and which left behind the lava flows, also created the Superior trough, a depressed region that became the basin of Lake Superior.
The lava flows formed the conditions for creation of Lake Superior agates. As the lava solidified, water vapor and carbon dioxide trapped within the solidified flows formed a vesicular texture (literally millions of small bubbles). Later, groundwater transported ferric iron, silica, and other dissolved minerals passed through the trapped gas vesicles. These quartz-rich groundwater solutions deposited concentric bands of fine-grained quartz called chalcedony, or embedded agates.
Over the next billion years, erosion exposed a number of the quartz-filled, banded vesicles—agates—were freed by running water and chemical disintegration of the lavas, since these vesicles were now harder than the lava rocks that contained them. The vast majority, however, remained lodged in the lava flows until the next major geologic event that changed them and Minnesota.
During the ensuing ice ages a lobe of glacial ice, the Superior lobe, moved into Minnesota through the agate-filled Superior trough. The glacier picked up surface agates and transported them south. Its crushing action and cycle of freezing and thawing at its base also freed many agates from within the lava flows and transported them, too. The advancing glacier acted like an enormous rock tumbler, abrading, fracturing, and rough-polishing the agates.
The Lake Superior agate is noted for its rich red, orange, and yellow coloring. This color scheme is caused by the oxidation of iron. Iron leached from rocks provided the pigment that gives the gemstone its beautiful array of color. The concentration of iron and the amount of oxidation determine the color within or between an agate’s bands.
The gemstone comes in various sizes. The gas pockets in which the agates formed were primarily small, about 1 cm in diameter. A few Lake Superior agates have been found that are 22 cm in diameter with a mass exceeding 10 kilograms. Very large agates are extremely rare.
The most common type of Lake Superior agate is the fortification agate with its eye-catching banding patterns. Each band, when traced around an exposed pattern or “face,” connects with itself like the walls of a fort, hence the name fortification agate.
A common subtype of the fortification agate is the parallel-banded, onyx-fortification or water-level agate. Perfectly straight, parallel bands occur over all or part of these stones. The straight bands were produced by puddles of quartz-rich solutions that crystallized inside the gas pocket under very low fluid pressure. The parallel nature of the bands also indicates the agate’s position inside the lava flow.
Probably the most popular Lake Superior agate is also one of the rarest. The highly treasured eye agate has perfectly round bands or “eyes” dotting the surface of the stone.
Occasionally, collectors find a gemstone with an almost perfectly smooth natural surface. These rare agates are believed to have spent a long time tumbling back and forth in the waves along some long-vanished, wave-battered rocky beach. They are called, appropriately enough, “water-washed” agates.
Cutting and polishing
A gemstone can be used as a jewel when cut and polished. Only a fraction of the Lake Superior agate are of the quality needed for lapidary. Three lapidary techniques are used on Lake Superior agates:
- Tumbling—Small gemstones are rotated in drums with progressively finer polishing grit for several days until they are smooth and reflective.
- Saw-cut and polish—Stones up to 1/2 kg are cut with diamond saws into thin slabs, which then are cut into various shapes. One side of the shaped slab is polished producing fine jewelry pieces and collectible gems called cabochons.
- Face polishing—Polishing a curved surface on a portion of the stone and leaving the major portion in its natural state is called face polishing.
Distribution of Lake Superior agate
One of the most appealing reasons for naming the Lake Superior agate as the Minnesota state gemstone is its general availability. Glacial activity spread agates throughout northeastern and central Minnesota, extreme northwestern Wisconsin and Michigan’s Upper Peninsula in the United States and the area around Thunder Bay in Northwestern Ontario, Canada.
Finding the gem
Typically the richly colored banding pattern is not well exposed and prospectors must look for other clues to the presence of agates.
The following characteristics are used to identify agates in the field.
- Band planes along which the agate has broken are sometimes visible, giving the rock a peeled texture. It appears as though the bands were partially peeled off like a banana skin.
- Iron-oxide staining is found on nearly all agates to some degree, and generally covers much of the rock. Such staining can be many different colors, but the most common are shades of rust-red and yellow.
- Translucence is an optical feature produced by chalcedony quartz, the principal constituent of agates. The quartz allows light to penetrate, producing a glow. Sunny days are best for observing translucence.
- A glossy, waxy appearance, especially on a chipped or broken surface, is another clue.
- A pitted texture often covers the rock surface. The pits are the result of knobs or projections from an initial layer of softer mineral matter deposited on the wall of the cavity in which the agate formed. Later, when the quartz that formed the agate was deposited in the cavity, these projections left impressions on the exterior.
The Oldest and Most Spectacular Mica, Feldspar,
Beryl, and Uranium Mine in the USA.
Open Weekends from
May 15 through June 6, 2010
June 12 through October 17, 2010
Children (4-11) $13
Children under 4 are Free with a paid adult.
July & August 9am-6pm
Last ticket sold 1 hour before closing
The mountains and valleys of New Hampshire are rich with mineral formations. From the southwest corner of the state near Keene to the northern Canadian border near Littleton there are fascinating deposits of a variety of minerals. One of these deposits is known as the Littleton Formation which was formed during the Devonian era approximately 300,000,000 years ago. The mining of these mineral deposits has been an important part of New Hampshire history from prehistoric eras to the present. The Ruggles Mine, in Grafton N.H., is part of the Littleton Formation and has a rich mining and geological history. It is the oldest and largest mine of its kind in the United States. Minerals such as Mica, Feldspar, Beryl, and Uranium were mined at Ruggles for 175 years.
Minerals and rocks fall into three classes of identification, metamorphic, igneous, and sedimentary. All of these mineral formations are found in New Hampshire. Metamorphic rock is formed under extreme conditions of heat and pressure. Igneous rock is formed when magma or molten rock cools and solidifies. Sedimentary rock is formed when wind or water deposit sediments and the sediments become compacted. Sedimentary and igneous rock can become metamorphic under certain conditions of intense heat and pressure in the crust of the earth. Metamorphic rock can also change into another type of metamorphic rock. Heat and pressure do not change the chemical makeup of parent rocks but they do change the mineral and physical properties of those rocks.
The Littleton Formation is classified as a metamorphic rock formation that was originally sedimentary. New Hampshire was at one time completely covered by the sea. As a result, huge amounts of sediment were deposited. Hadley and Chapman describe what occurred during the prehistoric era in New Hampshire.
How Rocks were Made
In early Devonian time, sand and mud were deposited. Thousands of feet, in alternating layers, accumulated to form the Littleton formation. William Barton explains what happened during the metamorphism. For untold years the sediments slowly accumulated on the ocean bottom. The earlier layers, compressed by continually increasing weight of newer overlying sediments, were changed into the sedimentary rocks called sandstone, siltstone, and shale. Eventually these layers of rock grew to be several miles in thickness. The Great Folding and the Rise of Molten Rock; Sometime near the close of the Devonian period, about 300,000.000 years ago, a period of great crustal unrest set in. Western New Hampshire, which for a hundred million had been dominantly a region of wide spread seas, began to be uplifted, never again to be covered by marine waters. This period was marked by two major phenomena; intense compression of the earth’s crust and the rise of molten rock into the crust.
Great compress ional forces, acting horizontally in a more or less east-west direction, squeezed the rocks and forced them to buckle. Gigantic folds, both upwards and downwards, trending north and south were produced.
The accumulation of buried sedimentary rocks were heated, squeezed into great folds, and shattered. The heat and pressure involved were so great that the mineralogical character of the rocks changed entirely. The new rocks were called metamorphic and were characterized by mica schists. The schishts consisted of mica and quartz, with the shiny mica flakes having formed from the pre-existing dull clay particles Without these enormous upheavals and pressure New Hampshire would not be as mineral rich as it is today.
The Littleton formation is primarily mica schist, and surrounds the Ruggles pegmatite. Although there are many pegmatites throughout the Littleton formation, the Ruggles Mine is unique because of its enormous size. The crystal formations within the Ruggles pegmatite are larger than any other ever discovered here in New Hampshire. It is 1640 feet long and 335 feet wide, and is approximately 250 feet deep.
Pegmatites are very coarse-grained igneous rocks, that is, those in which the grains range in size from 5 millimeters to 3 centimeters. The course grain results from the presence of volatiles during the crystallization, thus permitting large crystals to grow; The Pegmatite is light colored because it consists almost entirely of light colored minerals: Plagioclase and perthite feldspars, quartz and muscovite mica.
Over one hundred and fifty minerals have been identified in the Ruggles Mine. The primary mineral of economic interest was mica. Books of mica as large as five feet in diameter have been discovered. Without human intervention, these mineral deposits would never have enriched N.H
The Discovery of Mica
Mica was first discovered in 1803 in Grafton N.H. by a man named Sam Ruggles. It is believed that his origins were English and that he was probably farming and homesteading when he discovered mica on his property. Sam Ruggles knew the value of the mica he had discovered and set forth the first and one of the largest mining operations of its kind in the United States.
For years it is believed that Sam Ruggles went to great lengths to keep the location of his mine a secret. Ruggles put his family to work extracting books of mica. Then, to prevent his neighbors from learning of his discovery, the mica was packed into wagons along with farm product sand transported by ox-team to Portsmouth, N.H. From there it was shipped to England, where it could be sold without arousing anyone’s suspicion as to its possible origin.
As the demand for mica increased, Ruggles would make special trips to Portsmouth in the dead of night, still hoping to keep the location of his mine a secret. There is speculation as to why Ruggles was so adamant about keeping his mine a secret. One possibility is that land was being claimed and not purchased in the early 1800s and there was an acre limit on how much land could be claimed each year. Ruggles may have been trying to claim enough land to cover the entire mountain top to ensure ownership of all the mica outcroppings. This illustrates the value of these resources to N.H.
In the early nineteenth century mica was in great demand for its use in many household products. Because mica is heat resistant and transparent, it was used for the windows in woodstoves and whale-oil lamps. Mica was also used in ships windows. Basically anything that is now made of glass was made of mica in the early 1800s.
By 1840 it was said that 600 to 700 pounds of mica were mined annually, valued at $1500. By 1869 production had increased tremendously, and in that year it was reported that seventy-five boxes weighing 350 pounds each had been mined, making a total of 26,000 pounds.
The production of mica continued to increase into the late 1800’s. The Ruggles Mine reported shipping 3,600 pounds in January of 1877. By the early to middle part of the twentieth century mica mining began to decline. In 1930 as little as 8,000 pounds of mica was mined annually in the United States.
Despite the decrease in production, the value of mica remained high. Clear sheets of mica were still sold at very high prices, and by the early 1930’s an estimated $12,000,000 worth of mica had been mined at the Ruggles Mine.
Later on mica was used as an electrical insulator. It does not conduct heat or electricity due to its molecular structure. Early electrical appliances, such as toasters had mica in them. Mica is still being used today in products from building materials to cosmetics. Mica is in cement blocks and asphalt roof shingles. It is also used in lipsticks and fingernail polish. Most anything that sparkles contains mica.
The Development of Ruggles Mine
The ownership of the Ruggles Mine has changed several times over the years. It is not certain who owned the mine after the death of Sam Ruggles and for much of the rest of the nineteenth century. In 1874, a man named J.W. Kelton is said to have owned and operated the mine. By this time the mica was no longer being hauled away in secret by ox-cart, but being transported out of Grafton by the railroad.
Feldspar was the second most predominant mineral to be of economic interest at Ruggles Mine. The American Minerals company began mining feldspar in 1912. Feldspar was used in the making of high grade ceramics. The Syracuse China company used feldspar in the glazes on their fine china for many years. It was also used in the enamel surfaces of early appliances such as stoves and refrigerators. Feldspar was also in the making of false teeth.
The Bon Ami Company owned and operated the Ruggles Mine between 1932 and 1959. They mined the feldspar for use their non-abrasive scouring powder and glass cleaner. The Bon Ami Company extracted approximately ten thousand tons of feldspar a year during their period of operation.
Beryl is another mineral that was mined at Ruggles Mine. Beryl is the principal ore of the metal known as beryllium. Beryllium is lighter than aluminum and stronger than steel. Today, beryllium alloys are used in atomic reactors, electrical components, and as metal on spaceships components used at NASA. At one time during the mining of Beryl, a mass of the mineral was discovered that filled three freight train cars.
During the twentieth century The Ruggles Mine was reworked several times for the scrap mica that was left behind during earlier operations. The large “books” of mica were no longer being mined, but the smaller amounts that were dumped into waste piles during earlier operations. As new uses for mica were discovered, the demand for it increased once again. It was no longer used for whale-oil lamps, as in days of Sam Ruggles, but now in wallpaper (for sheen effect), paints, roofing, molded insulation, lubricants, etc. All the better grades were used for electrical insulation. The reworking of the mine was done by the English Mica Company of New York. They set up an extensive operation that crushed, screened, and washed the rock to separate it from the mica. The recovered mica was then washed down 3,200-foot flume to a mill at the bottom of the hill.
The Mine remained active and productive for 160 years. In the early 1960’s the U.S. government discontinued subsidizing the mica industry though it’s Mica Stock Piling Program. The result was that domestic mica mining operations could no longer compete in price with the mica imported from Brazil and India. Mining operations were thus discontinued at the Ruggles Mine.
The end of mining mica and other minerals ended an important chapter in the history New Hampshire. Mining provided employment and revenue to many people during the early days of our state. It provided our ancestors with an option to farming as means of survival. The Littleton Formation and the Ruggles pegmatite are what is left of a very significant part of geologic history. The formation was a natural resource that provided income and numerous minerals used in many important products.
In 1963 the Ruggles Mine was opened to the public. For 40 years visitors have been able to come and experience a part of this geologic and mining history. When entering the mine today one can still see where the feldspar and mica of the pegmatite connects to schist of the Littleton formation. One can witness the tremendous forces of the earths folding by observing the layers of schist that stand vertically above the pegmatite. The collecting of minerals is permitted at the Ruggles Mine, one can take home pieces of this history. Exploring the enormous caverns and tunnels provides insight into an event that took place 350,000,000 years ago. A visit to Ruggles provides insight into an important part of mining and geologic history.
A pegmatite is a very coarse-grained, intrusive igneous rock composed of interlocking grains usually larger than 2.5 cm in size; such rocks are referred to as pegmatitic.
Most pegmatites are composed of quartz, feldspar and mica; in essence a granite. Rarer intermediate composition and mafic pegmatites containing amphibole, Ca-plagioclase feldspar, pyroxene and other minerals are known, found in recrystallised zones and apophyses associated with large layered intrusions.
Crystal size is the most striking feature of pegmatites, with crystals usually over 5 cm in size. Individual crystals over 10 meters across have been found, and the world’s largest crystal was found within a pegmatite.
Similarly, crystal texture and form within pegmatitic rock may be taken to extreme size and perfection. Feldspar within a pegmatite may display exaggerated and perfect twinning, exsolution lamellae, and when affected by hydrous crystallization, macroscale graphic texture is known, with feldspar and quartz intergrown. Perthite feldspar within a pegmatite often shows gigantic perthitic texture visible to the naked eye.
Crystal growth rates in pegmatite must be incredibly fast to allow gigantic crystals to grow within the confines and pressures of the Earth’s crust. For this reason, the consensus on pegmatitic growth mechanisms involves a combination of the following processes;
- Low rates of nucleation of crystals coupled with high diffusivity to force growth of a few large crystals instead of many smaller crystals
- High vapor and water pressure, to assist in the enhancement of conditions of diffusivity
- High concentrations of fluxing elements such as boron and lithium which lower the temperature of solidification within the magma or vapor
- Low thermal gradients coupled with a high wall rock temperature, explaining the preponderance for pegmatite to occur only within greenschist metamorphic terranes
Despite this consensus on likely chemical, thermal and compositional conditions required to promote pegmatite growth there are three main theories behind pegmatite formation;
- Metamorphic; pegmatite fluids are created by devolatilisation (dewatering) of metamorphic rocks, particularly felsic gneiss, to liberate the right constituents and water, at the right temperature
- Magmatic; pegmatites tend to occur in the aureoles of granites in most cases, and are usually granitic in character, often closely matching the compositions of nearby granites. Pegmatites thus represent exsolved granitic material which crystallises in the country rocks
- Metasomatic; pegmatite, in a few cases, could be explained by the action of hot alteration fluids upon a rock mass, with bulk chemical and textural change.
Metasomatism is currently not well favored as a mechanism for pegmatite formation and it is likely that metamorphism and magmatism are both contributors toward the conditions necessary for pegmatite genesis.
The mineralogy of a pegmatite is in all cases dominated by some form of feldspar, often with mica and usually with quartz, being altogether “granitic” in character. Beyond that, pegmatite may include most minerals associated with granite and granite-associated hydrothermal systems, granite-associated mineralisation styles, for example greisens, and somewhat with skarn associated mineralisation.