Q: What is agate? Is it the same as jasper?
A: Agate is one of the more common types of semi-precious gemstones,
so much so that you may not realize how many of the articles you have seen
are made of some type of agate. Agate is a form of the mineral chalcedony,
which consists of an aggregate of very tine quartz crystals. If it is deposited
from water solutions and forms a translucent or transparent layered material,
we call it agate. If it's more uniform, less transparent, and non-layered
it's often called jasper (or for non gem types, flint and chert.) The layers
may be of varying colors, and much agate is striped in attractive patterns,
or has complex patterns of whorls and swirls. Carnelian and Sardonyx are
types of agate, often from Brazil, but it also comes from India and other
sources. A common type is Brazilian agate, which occurs often as sizeable
geodes, forming layered nodules. Often these are brownish tones, layered
with white and gray.Slices five and six inches across are common, which
are often polished as-is and sold as novelties. The stuff is also cut into
bowls and decorative articles of all types. It is often dyed in other colors.
Most of the commercially sold "black onyx" on the market is actually
brazilian agate, dyed black. A variety of sometimes colorful, sometimes
nondescript agates are common in India, and are often cut into very inexpensive
"beggar beads". Better samples can be cut into sometimes quite
spectacular and beautiful stones. Mexico produces a number of interesting
agates. One of the best known types is "crazy lace", which looks
just like a lacy, crazy, pattern of mixed up whorls and swirls and lines.
Its naturally usually whites and greys, but is often dyed all sorts of garish
colors as well. Plume agates are less layered looking but have inclusions
in them that can look like ferns, feathers, flames, or just about anything
else. These are sometimes quite spectacular, and sometimes rare and expensive,
for specific well known types. Montana agate is known for its basically
translucent white to transparent clear colors, with suspended black or brown
dots, swirls, or dendritic inclusions. It can be very pretty stuff, and
is often cut into cabochons, sometimes as beads.
Lake Superior agate has a tightly layered pattern, with narrow, often quite
contrasty banded layers, occurring usually in smallish nodules. Moss agate
looks just like moss, often dark green, sometimes with mixed-in reds and
browns, growing in the slightly cloudy to white base material. If the "moss"
is dense enough as to eliminate the white, making it an opaque solid green,
sometimes with red spots, we call it bloodstone, an alternate birthstone
for March. The above descriptions only begin to scratch the surface of the
subject. Agate occurs in hundreds, if not thousands of variations, and some
entire collections are made up of nothing else. One book on the subject,
called (I think) Agates of North America, by John Sinkankas, is a good start
to learning about some of what's out there. Or you can visit any decent
rock and mineral shop, most have a lot of different kinds on hand.
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