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<p>[QUOTE=&quot;spirit-of-shiloh, post: 12616, member: 32&quot;]Chalcedony is a generic name given to any material that is composed of microcrystalline quartz. Agate and jasper are both varieties of chalcedony.</p><p><br /></p><p>What is microcrystalline quartz? “Quartz” is a mineral composed of silicon and oxygen (SiO2) and the word microcrystalline means that the quartz is in the form of crystals that are smaller than 30 microns in size (a micron is a unit of measure that is 1/1000th of a millimeter). These are very tiny quartz crystals – smaller than can be seen by the unaided eye. (Sometimes the word “cryptocrystalline” is used instead of “microcrystalline.”)</p><p><br /></p><p>Chalcedony is a very hard material. It has a hardness of 7 on the Mohs scale. It breaks with a conchoidal fracture, and freshly broken pieces have a very smooth, non-granular texture and a waxy to vitreous luster. These characteristics enable chalcedony to be cut and polished into a bright, durable gemstone.</p><p><br /></p><p>Chalcedony occurs in a wide range of colors. It is often gray, white, brown, red, yellow, orange and black, but it can occur in any color. It can also be banded or have plume, dendritic, mottled, mossy or other color patterns. At one time the word “chalcedony” was reserved in parts of the gemstone industry for a light blue translucent material; however, this use of the word has nearly disappeared.[/QUOTE]</p><p><br /></p>

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