Agate

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Agate
Mossagate.pebble.750pix.jpg
Moss agate pebble, 2.5 cm (1 inch) long
General
Category Quartz variety
Chemical formula Silica, SiO2
Identification
Color White to grey, light blue, orange to red, black.
Crystal habit Cryptocrystalline silica
Crystal system Rhombohedral Microcrystalline
Cleavage None
Fracture Conchoidal with very sharp edges.
Mohs Scale hardness 7
Luster Waxy
Refractive index 1.530-1.540
Birefringence up to +0.004 (B-G)
Pleochroism Absent
Streak White
Specific gravity 2.58-2.64

Agate is a kind of quartz and it is a mineral. Agate can come in many different kinds and colors.