Agate
Moss agate pebble, 2.5 cm (1 inch) long
General
Category	Mineral
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 type of quartz (silica), chiefly chalcedony, characterised by its fineness of grain and brightness of color. Although agates may be found in various kinds of rock, they are especially common in metamorphic rock.

The colorful agate and other chalcedonies were obtained over 3,000 years ago from the Achates River, now the Drillo, in Sicily.

Agate - Wikipedia, the free encyclopedia

Agate is a term applied not to a distinct mineral species, but to an aggregate of various forms of silica, chiefly chalcedony. According to Theophrastus, the agate (achates) was named from the river ...

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Agate

Agate: banded beauty No gemstone is more creatively striped by Nature than agate, chalcedony quartz that forms in concentric layers in a wide variety of colours and textures.

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