Agate

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Agate
Mossagate.pebble.750pix.jpg
Moss agate pebble, 2.5 cm (1 inch) long
General
CategoryQuartz variety
Formula
(repeating unit)
Silica, SiO2
Identification
ColorWhite to grey, light blue, orange to red, black.
Crystal habitCryptocrystalline silica
Crystal systemRhombohedral Microcrystalline
CleavageNone
FractureConchoidal with very sharp edges.
Mohs scale hardness7
LusterWaxy
StreakWhite
Specific gravity2.58-2.64
Refractive index1.530-1.540
Birefringenceup to +0.004 (B-G)
PleochroismAbsent

Agate is a kind of quartz and it is a mineral. Agate can come in many different kinds and colors. Agate deposits are primarily found in large rocks such as boulders. agates take 50 million years to form. It is characterized by colored band patterns inside various rocks. Often, agates are also accompanied by Amethyst deposits inside as well as Quartz-like crystals occurring in larger deposits.[source?]