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A rich seam of iridescent opal encased in matrix
A rich seam of iridescent opal encased in matrix
Main opal producing countries
Main opal producing countries
Precious opal consists of spheres of silica molecules arranged in regular, closely packed planes (idealized diagram).
Precious opal consists of spheres of silica molecules arranged in regular, closely packed planes (idealized diagram).
This precious rough opal from Coober Pedy, South Australia, displays nearly every color of the visible spectrum.
This precious rough opal from Coober Pedy, South Australia, displays nearly every color of the visible spectrum.
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Crystals of serandite, natrolite, analcime, and aegirine from Mont Saint-Hilaire, Quebec, Canada
Crystals of serandite, natrolite, analcime, and aegirine from Mont Saint-Hilaire, Quebec, Canada
Schist is a metamorphic rock characterized by an abundance of platy minerals. In this example, the rock has prominent sillimanite porphyroblasts as la
Schist is a metamorphic rock characterized by an abundance of platy minerals. In this example, the rock has prominent sillimanite porphyroblasts as large as 3 cm (1.2 in).
Hübnerite, the manganese-rich end-member of the wolframite series, with minor quartz in the background
Hübnerite, the manganese-rich end-member of the wolframite series, with minor quartz in the background
When minerals react, the products will sometimes assume the shape of the reagent; the product mineral is termed a pseudomorph of (or after) the reagen
When minerals react, the products will sometimes assume the shape of the reagent; the product mineral is termed a pseudomorph of (or after) the reagent. Illustrated here is a pseudomorph of kaolinite after orthoclase. Here, the pseudomorph preserved the Carlsbad twinning common in orthoclase.