Agates are part of the Chalcedony Species (see) and are considered cryptocrystalline quartzes. There are many types of Agates and they are found all over the world.
Dendritic Agate is a colorless or whitish-gray, translucent stone with tree-like or fern-like markings. These are not fossilized plants. The dendrites are iron or manganese inclusions. In Scenic Agate, the dendrites resemble landscapes. The Scenic Agates are highly prized by collectors and usually fetch fairly high prices.
Moss Agate has dense inclusions of green hornblende.
Tree Agate is white or off-white with green flecks.
Botswana Agate comes from Botswana in Africa. It has very fine bands of tan, brown, pink and white. It has been almost completely mined out.
Crazy Lace Agate has crazily twisted and turned bands and occurs in a host of colors (yellow, brown, red, orange). There are some very nice color enhanced Crazy Lace Agates on the market that hold their color very well.
Blue Lace Agate is light blue with wavy bands of white or lighter blue.
Golden Agate is a mottled golden color with the occasional bit of "chalcedony blue".
Montana Agate is prized for the scenes that occur in it. It is a very pricey agate.
As with Jaspers, there are new Agates coming onto the market all the time. The naming of these newer Agates can be confusing since the names are mostly not trade marked and are simply names that the cutting houses have applied to a particular product. There is one "Jasper" that is actually an Agate, but has been trade marked "Ocean Jasper".
crazy lace, red crazy lace and lace agates
Amethyst
Amethyst is a Quartz (silicon dioxide) and occurs in shades of purple, violet and pale red-violet. A variety that was popular many years ago called "Rose de France", has become popular again. It is a very pale violet and is sometimes called Pink Amethyst.
Heat treating Amethyst produces colors in the range of light yellow (Citrine), green (Prasiolite) or red-brown. The green variety, currently called Green Amethyst, has also recently become popular.
Amethyst occurs in Brazil and Uruguay (some of the finest), Africa (very dark and very fine), Myanmar (Burma), India, Mexico, Arizona and Russia, to name a few.
Crystals that exhibit both the Amethyst and Citrine colors are called Ametrine.
an amethyst cabochon set in sterling silver
Carnelian (see Chalcedony)
Carnelian belongs in the Chalcedony Species. It is thought that it was named for the color of the kornel cherry. Some people still call it "Kornelian". But more often, that name is applied to Carnelian that has been heated to significantly darken its color.
It is found in Brazil, India and Uruguay.
Some Carnelian will show banding like Agate (also a Chalcedony).
Sard is a red-brown variety of Chalcedony and is usually darker and browner than Carnelian.
Sardonyx is a name usually applied to a carnelian that has strong white banding.
Banded Carnelian
Carnelian cabochon
Chalcedony
Chalcedony is used by gemologists as a species name for all the cryptocrystalline quartzes: Agate (see), Petrified Wood, Chrysoprase, Bloodstone, Jasper (see), Carnelian (see), Moss Agate (see Agate), Onyx and Sard (see Carnelian).
Most people consider Chalcedony to be only the bluish-white-gray variety. It is a silicon dioxide as are all quartzes.
There are a lot of color enhanced Chalcedonies on the market right now. It is best to steer clear of them as they tend to fade when exposed to sunlight.
Sometimes Chalcedony is confused with Blue Lace Agate (see Agate), which is similar in color but displays the banding typical of Agate. Apple green Chalcedony is called Chrysoprase.
Color enhanced chalcedony cabochons
Blue Chalcedony with a natural surface
Citrine
Citrine is a quartz (silicon dioxide). It is a lemon yellow color. It can sometimes be very pale or brownish.
Natural Citrine is relatively rare. Most Citrines are heat treated to produce the color (see Amethyst). Almost all heat treated Citrines have a reddish tint. The natural Citrines are a pale yellow.
Deposits of natural colored Citrines are found in Brazil, Madagascar, USA, Argentina, Burma (Myanmar), Namibia, Russia, Scotland and Spain.
Natural Citrine Crystal
Faceted Citrine
Copper
The abbreviation for copper on the chart of elements is Cu. Its natural color is a copper-red that tarnishes black. It will occur in ores as a blue or green color. Native copper (it looks like copper when you come across it) develops in basalt of volcanic rocks. It is usually associated with cuprite and calcite. Some of the copper mines in Arizona have yielded spectacular specimens of native copper. Native copper can also be found in New Mexico, Oregon, Alaska, New Jersey and Nova Scotia. Arizona is known as the Copper State.
The name is derived from the Greek Kyprios, the island Cyprus, where copper was early found and mined.
Copper is the first metal to be mined and used by early man. This is mainly because it is so plentiful and required very little mining to obtain. Also, native copper requires very little to no refining to make it useable.
Native Copper
Coral
Coral is considered an organic gemstone. Coral is a branching skeleton-like structure built by the secretions of coral polyps. Coral occurs naturally in colors of red, pink, white, black and blue. However, most Coral on the market today has been color enhanced with an oil based dye.
In Tucson, I saw some gold Coral. This is black coral that has been treated (not bleached, however) and then coated. It's very pretty, but I didn't buy any. I was unsure about its wear ability.
There are also Sponge Corals and China Deep Sea Corals. Supposedly, these are not color enhanced.
Some of the finest Coral is said to come from the Mediterranean Sea. Pink Angel Skin Coral is one of my favorites.
Dyed Branch Coral
Dyed Bamboo Coral
Druse
Druse is a term used to describe crystals that form on the inner walls of rock openings (geodes). These are mainly round hollows created by gas bubbles in magma.
We can speak of a quartz druse or describe a quartz as "drusy quartz". But most often, today people simply say "drusy" (sometimes spelled "druzy") when they mean a crust of small crystals on a base surface.
In fact, druses can be quite large as in Amethyst crystals.
Some "drusies" have been treated with various metals to give them a gold luster or a peacock blue color.
Just about all minerals with a crystalline structure can form druses.
