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01/28/09
frame silicates

The frame silicates are exciting for the average rockhound.  It is these minerals that brought a lot of people into the business/hobby.

The silica group of frame silicates includes free silica in large crystals, cryptocrystalline varieties (grains can only be seen in a microscope), and amorphous silica containing water.

Quartz is everywhere.  Its uses are many:  firebrick, gemstones, electronics, and it is the principal component of glass.  Most people are familiar with the hexagonal structure of a quartz crystal.  Cryptocrystalline quartz starts out as amorphous gel and the water settles out, leaving colorful banded and patternes materials that have been given separate names.

Chert is the duller, more opaque variety of cryptocrystalline quartz.  Jasper is one of its subcategories.  Jasper can be any color but is usually brightly colored and patterned.  Flint is a black variety of chert.  Aventurine is chert with mica particles that make is sparkly.  Cherts are useful for making stone tools such as arrowheads, due to their conchoidal fracture.


Chalcedony is the more translucent variety of cryptocrystalline quartz.  Gem varieties of onyx are agate, onyx, sardonyx, tigereye, carnelian and chrysoprase.


Posted by oh5/ojhoff at 11:26 AM CST
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