Quartz - Wikipedia, the free encyclopediaQuartz is the second most abundant mineral in Earth's continental crust, after feldspar. Its crystal structure is a continuous framework of SiO4 silicon–oxygen .. unaided eye) and the microcrystalline or cryptocrystalline varieties (aggregates of crystals . It is a rare stone in nature, most green quartz is heat-treated amethyst.microcrystalline stone structure,Agate - Wikipedia, the free encyclopediaAgate /ˈæɡət/ is a cryptocrystalline variety of silica, chiefly chalcedony, characterised by its . Crystal system · Rhombohedral Microcrystalline. Identification . Such stones are known as banded agate, riband agate and striped agate.Gemstone Terminology - Earthmother CraftsAgate, Jasper, Onyx and Carnelian are all members of the microcrystalline and/or . It is not actually a stone, but rather the calcified structures of once living tiny.
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