Kyanite, whose name derives from the Greek word kyanos, meaning blue, is a typically blue silicate mineral, commonly found in aluminium-rich metamorphic pegmatites and/or sedimentary rock. Kyanite is a diagnostic mineral of the Blueschist Facies of metamorphic rocks.
Kyanite is a member of the aluminosilicate series, which includes the polymorph andalusite and the polymorph sillimanite. Kyanite is strongly anisotropic, in that its hardness varies depending on its crystallographic direction. While this is a feature of almost all minerals, in kyanite this anisotropism can be considered an identifying characteristic.
Uses of kyanite
Kyanite is used primarily in refractory and ceramic products, including porcelain plumbing fixtures and dinnerware. It is also used in electrical insulators and abrasives. Kyanite is important enough an ore that a mining company, the Kyanite Mining Corporation focuses on its processing and refinement. Kyanite has also been used as a gemstone, though this use is limited by its anisotropism and perfect cleavage. Finally, as with most minerals, kyanite is a collector’s mineral.
Outside of Philadelphia, behind a baseball field quality kyanite can be obtained. But don’t forget to bring your rubber gloves!
Prospect Park is a town that lies 11 miles south west of the city of Philadelphia and it is located right along the merge of I-95 and I-476, a good spot for city growth! Most of the growth in the area is in housing, so it is unlikely this site will ever be closed off, due to it’s location next to a place called Morton Homestead. Morton Homestead is protected state owned example of the typical early Swedish cabins built along the coast of Pennsylvania. So, the first couple times I got lost looking for this spot I would just think to myself, “Those Swedish immigrants sure knew how to build a solid house.” while I looped around it a couple times.
This location for Kyanite is located in the creek directly behind Morton Homestead, along the side of a baseball field (and the parking lot next to it). The best way to get to this location is by parking in the baseball field parking lot and walking into the woods into the small trickle of water that is the home to this mineral!
The majority of the trash is at the end the creek, but the best kyanite comes from the beginning of the creek. Matter of fact, bring a trash bag and collect a bag of trash while you are at it. It’s not FUN, but hey, you are there getting free rocks, right? Well, what better trade for yourself and the environment than to pick up a bag of trash on your way out. There are dumpsters near the baseball field. The best technique for finding nice specimens is to scour the coast first and look for the bright blue material in the semi-calm water. Next, start turning over material in the stream with a hoe and let the dirt settle and repeat looking for more blue flashes. It works great. The last time I was there we used that technique and brought home a 2 gallon bucket of great gemmy blue material, lots of single blades, but some excellent clusters as well. A few months after that dig I read an article in Rock and Gem magazine about this location, but the writer lamented about not finding much good material, besides lots of black kyanite. Well, he went there within the week of us picking up all the easy stuff for that month. New material is being weathered out of the ground from the deposit, directly under the stream. After big rains in the area are surely the best times to go collecting here!
To get to this location take I 95 to exit 9, Wanamaker Ave/Rt. 420, Lincon Ave NW. The road will split in two, and then come back together again, at which point you should turn left. This road takes you directly to a baseball field. Park in the parking lot, walk into the woods and you are there.
Kyanite is usually found in association with its polymorphs, as well as other silicate minerals. These include:
- andalusite, Al2SiO5
- sillimanite, Al2SiO5
- quartz, SiO2
- staurolite, Fe2Al9Si4O22(OH)2
- micas, AB2-3(X, Si)4O10(O,F,OH)2
- garnets, A3B2(SiO4)3
Kyanite has several alternative names, including disthene, munkrudite and cyanite. White-grey kyanite is also called rhaeticite.
Notes for identification
Kyanite’s elongated, columnar crystals are usually a good first indication of the mineral, as well as its color (when the specimen is blue). Associated minerals are useful as well, especially the presence of the polymorphs or staurolite, which occur frequently with kyanite. However, the most useful characteristic in identifying kyanite is its anisotropism. If one suspects a specimen to be kyanite, verifying that it has two distinctly different hardnesses on perpendicular axes is a key to identification.