Gems of Interest – Other Gem Materials

There are many minerals accepted as gem materials. Some gem materials are organic in origin rather than mineral, such as amber and coral.

Here are some additional gems of interest you may encounter on your gem quest.

Minerals and Other Gem Materials

Amber

Amber is the fossil resin of ancient pine trees. By ancient I mean a mere twenty to thirty million years ago! The most interesting pieces of amber contain a fossilized ancient insect or leaf; these pieces are the most valued.

Amber is found in yellow, gold, orange, brown and rarely in bluish and greenish shades. Amber can be easily identified because it is so lightweight. Technically this means it has a very low specific gravity. A piece of amber will float in concentrated salt solution. Plastic imitations will not do this. Amber is a soft material, with a hardness of around 2 to 21/2. It will be easily scratched and should be worn and stored with care. Amber has a low melting point and can be pressed into larger pieces or molded in to shapes when it is soft. Pressed amber pieces will be less expensive. As amber ages it may turn red or pressed amber may take on a white cast.

Amber is found in a variety of places: Baltic amber is found floating in the Baltic Sea: some amber is dug from pits. Some amber is found in the Dominican Republic.

Amber will range in price from low to expensive; the highest prices will be for the most unusual pieces bearing some long dead creature. Most amber is very affordable. Fine bead strands in a large size with pleasing color will fall in the moderate category. Fine amber jewelry may be antique and command a higher price for that reason.

Apatite

Apatite has appeared on the gem markets of the world as a very affordable substitute for Paraiba tourmaline. Canada is the source for the intense sea-blue and green stones can be easily mistaken for the much more expensive tourmalines. Neon describes the color intensity. Apatite is also found in colorless, pale yellow and pastel violet colors. Occasionally apatite is found with a fibrous structure and is cut in cat's-eye cabochons. Apatite deposits occur in Burma, Spain, Mexico, California, Sri Lanka, Mozambique, Madagascar, Brazil, and India. Despite its many sources, few are available to the gem market.

(Apatite trillion 4.22 carat, photo by David Dikinis)

As beautiful and affordable as the exquisite apatites are, they only have a hardness of 5 on Moh's scale. Perfect for earrings and pendants, they lack the durability for a ring stone. Most apatite are cut into small gemstones weighing one carat or less and fall into the low end price range. Stones from two to five carats are quite rare and would most likely fall into a moderate price range. Exceptional stones- large and very intense in color- could command higher prices if you could find one.

Azurite

Azurite is a deep intense blue copper bearing mineral. Very rarely it can be found in small transparent crystals or in small geodes with tiny crystalline pockets of azurite along with other minerals. Most pieces are cut into cabochons. Frequently azurite is combined with malachite; the result of this marriage is a unique stone with deep blue combined with dark green.

Generally small azurite cabochons will fall into the low price range. Larger or unusual pieces may be moderate in price. It is not normally sold by the carat, but by the piece. Azurite has a hardness of about 31/2 to 4; handle it with care.

Benitoite

Benitoite was mistaken for fine blue sapphire when it was first found in California in 1906! Benitoite is the official state gemstone for California; its only known source is in San Benito County. Unfortunately the gemstone is very rare and those not living in California may never have the chance to see one.

Benitoite, 2.28 carats, San Benito County, California (Photo by ICA/Bart Curren)

Even California residents will have to search to find one. The color of benitoite, in the best qualities, is a medium dark blue. It has a high dispersion that is difficult to see in the darker blue stones. The hardness is 6 to 61/2 and it is brittle, so it must be set into protective settings with care if worn as a ring stone. Benitoite is available in small stones, usually one carat or less, with the largest one in the Smithsonian weighing about 7.80 carats. Fine quality stones will be in the expensive range.

Calcite

Calcite is rarely cut into gemstones; it is soft with a hardness of 3 and it has perfect cleavage in three directions which makes it is quite difficult to cut. A banded variety of calcite generally found as stalagmites is called onyx marble; it may be incorrectly referred to as "Mexican onyx." This material is carved into all sorts of things like chess sets, boxes or in candlesticks, especially in Mexico, and is low in price. "Iceland spar" is a colorless form of calcite found in Iceland. It forms fascinating crystals. If you put a piece of Iceland spar over print and look through it the print will appear doubled. Calcite is the most birefringent gem material and that is an easy way to observe birefringence. Calcite is commonly dyed and sold as cheap beads and other jewelry items in Mexico.

Coral

Coral is composed of the skeletons of sea creatures, the "coral polyp." Coral grows in warm waters in various seas. The finest coral is red coral from the Mediterranean. Coral is found in seas around Japan and Hawaii and many other locations. Coral comes in a variety of colors: white, pinks, orangy-pinks, red-oranges, and black. Coral is carved or cut into beads or cabochons.

(Coral photo by ICA/Bart Curren)

The deep orange-red material is called "oxblood" and is the highest priced of the corals. Soft pink material is called "angel's skin." Coral has a hardness of 3 1/2 to 4, so treat it gently. Coral will range in price depending on its color, size, and the quality of any carving. A small cabochon may be low in price; large fine beads or beautiful fine cameos will be in the moderate to expensive classification.

Diopside

Diopside is a mineral occurring in a few colors, but a stone you might encounter is chrome diopside. The most desirable chrome diopside comes in a brilliant spectacular green color; it can easily be mistaken for chrome tourmaline. It is low in price for small stones but fine larger pieces may hit the moderate per carat prices. It has a hardness of 5 1/2 to 6 1/2 and it is brittle with perfect cleavage so it should be set with care. It is a good choice for earrings. You may occasionally find diopside in "star" and "eye" stones.

(Chrome diopside photo by ICA/Bart Curren)

Fluorite

Fluorite comes in some magnificent colors: violet, bright green, blue, yellow, orange, and pink. But as a faceted gem fluorite is too fragile to be wearable. It has a hardness of 4 with perfect cleavage in four directions; often pieces are filled with cracks. It is a material that can be beautiful when cut into beads. Crystals of fluorite are pretty just to look at because they come in perfect natural tetrahedrons. Beads are affordable.

Hematite

Hematite is a metallic appearing dark gray material that is cut into beads, cameos, intaglios and cabochons. It is actually an iron ore. It is quite heavy. Most hematite will be in the very affordable range.

Jet

Jet is not a mineral but a fossilized coniferous wood. Actually it is a lignite coal and will burn! Jet was very popular in mourning jewelry during the Victorian Period, but it is rarely used today. If you are looking at antique jewelry, the age, craftsmanship of the piece will affect the price more than the jet itself. It is a soft material, hardness of 2 1/2 to 4 and brittle so handle it carefully.

Kyanite

Kyanite is an interesting gem: it is color-zoned in shades of blue and blue-green. Most material is visibly included. Most kyanite is from Brazil but it is also found in Africa. It has a hardness that ranges from 4 to 7.5; this extreme variable hardness as well as perfect cleavage makes it difficult to cut. Faceted stones are generally under five carats but can be found up to twenty carats. This is a collector item and price will vary depending on size, color, and clarity. Ordinary ones should fall in the low price per carat category, but exceptional ones will be more.

Malachite

Malachite is an opaque green copper mineral. It is banded in different shades of green and can be cut into interesting patterns. Malachite is found in large pieces and is often carved into decorative objects and cut into beads and cabochons. Small beads and cabochons will be low in cost. Other decorative items will be priced according to size and workmanship. Most malachite is mined in Democratic Republic of Congo and Zambia. Malachite is often found with azurite: these combination blue and green pieces are a unique gem material. Malachite is soft, with a hardness of 31/2 to 41/2 and it must be kept away from acids. Don't clean it in ammonia, it could discolor.

Obsidian

Obsidian is a volcanic glass that usually comes in black or brown; some has inclusions that give it a sheen. Snowflake obsidian has a white inclusion that looks like a "snowflake" This is a very inexpensive gem material which can be found in the western United States near volcanoes. Obsidians are cut into beads and other decorative objects and should be very affordable.

Rhodochrosite

Rhodochrosite is a pink to orange to red gem material that has a magnificent intensity when it is transparent. It can be faceted, but is very fragile and impractical for jewelry use. The hardness is only 31/2 to 41/2 and the stone is brittle. Translucent rhodochrosite is cut into beautiful beads and cabochons. Some material is more opaque and banded. Rhodochrosite beads will range in price depending on size, color, and translucency. Prices will start on the low side and nice qualities will be in the moderate range.

Rhodonite

Rhodonite is an opaque pink material that usually has black streaks. It is cut into beads and cabochons; these will be very affordable. Rhodonite may also be carved into decorative objects. It has a hardness of 5 1/2 to 6 1/2.

Scapolite

You won't find scapolite without looking, but there are some beautiful yellow, violet and pink ones out there for the avid gem hunter. It does come in a few more colors and in cat's-eye form but these are really hard to find. Scapolite is mined in Brazil, Kenya, and Myanmar (Burma). It has a hardness of 6. It will be moderate in price unless stones are small or very pale in which case they will be low in price.

Sodalite

Sodalite is a dark blue mineral that can easily be confused with lapis lazuli. It is one of the mineral components of lapis lazuli. Some sodalite has calcite streaks. Sodalite can be semi-transparent to opaque. It is cut into beads and decorative objects and will be very affordable. It differs from lapis lazuli which is a "rock" containing calcite and pyrite.