RockHoundBlog

Salted Mine

Filed under: Rockhound Dictionary — Gary November 8, 2010 @ 9:39 pm

Salted is an interesting rockhound term. It’s used by fellow rockhounds to describe a mine company that “enriches” the earth around/in the mine with gems/minerals that may or may not be native to that mine. Some mine companies tout it as a good thing and if they are up front and honest about what they are doing then it’s alright I believe (so everyone can find a gem/mineral when they go hunting – they payed for it right???).
Although there are other mine companies that do it quietly and tell no one. Is this fair/ethical? You can decide for yourself I guess.

Matrix (geology)

Filed under: Rockhound Dictionary — Gary October 17, 2010 @ 9:43 pm
RARE SILVER!!! Sharp, lustrous crystals of Acanthite on Quartz matrix!   It comes from the Victor Mine which was part of the Tonopah Extension Company in Tonopah, Nevada and dates to 1906-1910.    A CLASSIC Nevada Silver specimen from the early Jim Butler days.

RARE SILVER!!! Sharp, lustrous crystals of Acanthite on Quartz matrix! It comes from the Victor Mine which was part of the Tonopah Extension Company in Tonopah, Nevada and dates to 1906-1910. A CLASSIC Nevada Silver specimen from the early Jim Butler days.

To buy this silver on matrix go here: http://www.exceptionalminerals.com/saleroom2.htm

The matrix or groundmass of rock is the fine-grained mass of material in which larger grains or crystals are embedded.

The matrix of an igneous rock consists of fine-grained, often microscopic, crystals in which larger crystals (phenocrysts) are embedded. This porphyritic texture is indicative of multi-stage cooling of magma. For example, porphyritic andesite will have large phenocrysts of plagioclase in a fine-grained matrix. Also in South Africa, diamonds are often mined from a matrix of weathered clay-like rock (kimberlite) called “yellow ground”.

The matrix of sedimentary rocks is a fine-grained clay or silt in which larger grains are embedded. It is also the rock material in which a fossil is embedded.

Cementations

All sediments are at first in an incoherent condition (e.g. sands, clays and gravels, beds of shells, etc.), and in this state they may remain for an indefinite period. Millions of years have elapsed since some of the early Tertiary strata gathered on the ocean floor, yet they are quite friable (e.g. the London Clay) and differ little from many recent accumulations. There are few exceptions, however, to the rule that with increasing age sedimentary rocks become more and more indurated, and the older they are the more likely it is that they will have the firm consistency generally implied in the term “rock”.

The pressure of newer sediments on underlying masses is apparently one cause of this change, though not in itself a very powerful one. More efficiency is generally ascribed to the action of percolating water, which takes up certain soluble materials and redeposits them in pores and cavities. This operation is probably accelerated by the increased pressure produced by superincumbent masses, and to some extent also by the rise of temperature which inevitably takes place in rocks buried to some depth beneath the surface. The rise of temperature, however, is never very great; we know more that one instance of sedimentary deposits which have been buried beneath four or five miles of similar strata (e.g. parts of the Old Red Sandstone), yet no perceptible difference in condition can be made out between beds of similar composition at the top of the series and near its base.

The redeposited cementing material is most commonly calcareous or siliceous. Limestones, which were originally a loose accumulation of shells, corals, etc., become compacted into firm rock in this manner; and the process often takes place with surprising ease, as for example in the deeper parts of coral reefs, or even in wind-blown masses of shelly sand exposed merely to the action of rain. The cementing substance may be regularly deposited in crystalline continuity on the original grains, where these were crystalline; and even in sandstones (such as Kentish Rag) a crystalline matrix of calcite often envelops the sand grains. The change of aragonite to calcite and of calcite to dolomite, by forming new crystalline masses in the interior of the rock, usually also accelerates consolidations. Silica is less easily soluble in ordinary waters, but even this ingredient of rocks is dissolved and redeposited with great frequency. Many sandstones are held together by an infinitesimal amount of colloid or cryptocrystalline silica; when freshly dug from the quarry they are soft and easily trimmed, but after exposure to the air for some time they become much harder, as their siliceous cement sets and passes into a rigid condition. Others contain fine scales of kaolin or of mica. Argillaceous materials may be compacted by mere pressure, like graphite and other scaly minerals.

Potassium feldspar crystals in a granite, eastern Sierra Nevada, Rock Creek Canyon, California.

Potassium feldspar crystals in a granite, eastern Sierra Nevada, Rock Creek Canyon, California.

Thanks wikipedia

Druze and Drusy

Filed under: Rockhound Dictionary,Video — Gary October 14, 2010 @ 9:57 am

Rockhound Terms

Drusy
Drusy (sometimes referred to as: druse, druzy) is a layer of tiny quartz crystals that form on a host stone (A gemstone with natural surface textured similar to fine sugar crystals.). The cavity inside a geode is sometimes filled with drusy quartz crystals. Although the quartz crystals may be the source of the color (amethyst, citrine), usually it is the host stone’s color (chrysocolla, uvarovite garnet) that shows through the quartz and gives the stone its color. (pronounced: dru-zee).  Drusy is created by the phenomena of micro-crystalline facets forming on a gem and the surrounding rock, they were formed naturally millions of years ago.

Druze
Druze is a layer of crystals that form within a mineral crust, like the inner cavity of a geode. Amethyst crystals are often found in a druze. The inner cavity of agate geodes are often lined with a druze of sparkling quartz crystals.

Lets call the whole thing off?  :)

RockHound Term

Filed under: Rockhound Dictionary,Video — Gary October 13, 2010 @ 10:15 pm

Chatoyancy

Chatoyancy

Chatoyancy

In gemology, chatoyancy (pronounced shə-TOY-ən-see), or chatoyance, is an optical reflectance effect seen in certain gemstones. Coined from the French “œil de chat,” meaning “cat’s eye,” chatoyancy arises either from the fibrous structure of a material, as in tiger eye quartz, or from fibrous inclusions or cavities within the stone, as in cat’s eye chrysoberyl. The effect can be likened to the sheen off a spool of silk: The luminous streak of reflected light is always perpendicular to the direction of the fibres. For a gemstone to show this effect best it must be cut en cabochon, with the fibers or fibrous structures parallel to the base of the finished stone. Faceted stones are less likely to show the effect well.

Gem species known for this phenomenon include the aforementioned quartz, chrysoberyl, beryl (especially var. aquamarine), tourmaline, apatite, moonstone and scapolite. Glass optical cable can also display chatoyancy if properly cut, and has become a popular decorative material in a variety of vivid colors.

The term Cat’s Eye, when used by itself as the name of a gemstone, can only be used to refer to a Cat’s Eye Chrysoberyl. Any other stone exhibiting this phenomenon must have the stone’s name after the Cat’s Eye identifier, i.e. Cat’s Eye Aquamarine.

Chatoyancy can also be used to refer to a similar effect in woodworking, where certain finishes will cause the wood grain to achieve a striking three-dimensional appearance. This effect is often highly sought after, and is sometimes referred to as “wet look”, since wetting wood with water often displays the chatoyancy, albeit only until the wood dries. Oil finishes and shellac can bring out the effect strongly.

Interesting video  – How light reacts with a gemstone