Agate

AGATE

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Agate is a cryptocrystalline variety of the mineral Quartz . Quartz is the most abundant single mineral on earth. It makes up about twelve percent 12 (%) of the earth's crust, occurring in a wide variety of igneous, metamorphic and sedimentary rocks.

Quartz varieties are commonly separated into two groups based on the size of the individual grains or crystals; macrocrystalline quartz in which individual crystals are distinguishable with the naked eye, and cryptocrystalline quartz in which the individual crystals are too small to be easily distinguishable under the light microscope.

The thickness of the agate bands can vary, but tend to stay consistent throughout a nodule. Sometimes if the cavity is not completely filled with agate, the center may contain crystals such as rock crystal, amethyst or smoky quartz.

Chemical Composition and Name	SiO2
Class	Tectosilicate
Crystal System	Hexagonal - R; 32 (trigonal - trapezohedral)
Crystal Habit	Usually as banded or layered botryoidal masses with microfibrous structure.

Zoning	Colour banding and layers of inclusions are common.
Specific Gravity	2.57 - 2.64
Index of refraction	1.53 - 1.55
Hardness	6.5 to 7

Colour	frequently colored by impurities and then may be any color, most agate used for ornamental purposes is colored by artificial means.
Luster	Dull vitreous to greasy
Transparency	Translucent, can be transparent or opaque

Cleavage

Cryptocrystalline quartz shows no cleavage, although parting may occur along layers and splintery fracture can develope parallel to microfibrous orientation.

Fracture	Conchoidal to splintery
Streak	White

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Agate Stocks)

SOURCES FOR THIS GEMSTONE

The most famous place that agate has been mined is Idar-Oberstein in Germany where it has been collected since 1548. Most agate today comes from the huge deposits in Uruguay and Brazil. Agate is also found in the United States, Mexico, Madagascar, Italy, Egypt, India, China, Scotland, Tanzania, Malawi.