Quartz
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Quartz is a hard mineral composed of silica. Its atoms are linked in a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen atom being shared between two tetrahedra, giving an over
Quartz crystal cluster from Brazil
Common, prismatic quartz
Sceptered quartz
Sceptered quartz (as aggregates: "Elestial quartz")
Agate
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Agate is a banded variety of fibrous chalcedony. Agate stones are characterized by alternating bands of different colored chalcedony and often contain some visible quartz crystals. They are common in
Polished agate nodule from Malawi
When backlit, thin slices of agate can occasionally show their fibrous structure as lines running perpendicular to the bands (top)
Agate exhibiting wall banding (top) and level banding (bottom)
Agate geode slice with macrocrystalline quartz and a hollow center