Agate is a variety of chalcedony in the quartz group. Prospecting and collecting agates is a
wonderful outdoor family activity. Lapidary work to cut and polish semi precious gemstones often
involves agates such as uses for gemstone guitar picks.
Colorado agate found, cut and polished by ColoradoProspector. Photo by Denise.
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Mohs hardness: 7
Common uses today - Usable and ornamental stone objects such as
stone guitar picks, jewelry, ink boats, and because of it's hardness and resistence to
acids it's used to make mortar and pestles.
From Wikipedia -
"Agate is a microcrystalline variety 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 classically associated with volcanic
rocks but can be common in certain metamorphic rocks.
Most agates occur as nodules in volcanic rocks or ancient lavas where they represent cavities
originally produced by the disengagement of volatiles in the molten mass which were then filled,
wholly or partially, by siliceous matter deposited in regular layers upon the walls.
Often agate coexists with layers or masses of opal, jasper or crystalline quartz
due to ambient variations during the formation process.
Because of the high polish possible with agate it has been used for centuries for leather burnishing tools."
"[Note: Many non-banded forms of chalcedony - such as Moss agate - are often erroneously called 'agates'.
True agate is concentrically banded. Mottled and included chalcedonies are more properly called simply
Petrified wood (agatized wood) is the name given to fossil wood where the replacement of
the wood is by chalcedony, but the banding in this case is due to the wood structure - not concentric
deposition of the chalcedony - and the material is chalcedony, not true agate.]"
Check out the Mindat.org database for detailed information about