Brown Gemstones: A Guide to Colored Stones

Smoky quartz is a brown, smoky-gray or black quartz gemstone that occurs when colorless rock crystal is exposed to natural radiation in the earth. Smoky quartz has gained popularity since the trend for cognac diamonds, but unlike brown diamonds, smoky quartz gemstones are affordable, even in large sizes. Unscrupulous gemstone dealers sometimes sell smoky quartz gemstones as "smoky topaz", which does not exist. Smoky quartz can be found in almost every shape and cut imaginable, making it extremely versatile.

Chocolate opal is a translucent to opaque opal variety from Ethiopia that forms within layers of volcanic ash in Yita Ridge; a small area northeast of the capital city, Addis Ababa. As its name suggests, chocolate opal has a distinctive chocolate brown color, which may be light- or dark-brown. Like precious opal, chocolate opal exhibits play of color and specimens with vivid and intense play of color are most valued, especially stones that display a range of colors.

Boulder opal is a valuable opal variety that is found embedded in large boulders of ironstone, in which precious opal forms in thin fissures, veins and hollows. It is also called "opal in matrix" because some of the matrix rock is preserved when the opal is removed and then cut into gemstones. The ironstone of boulder opal gemstones is opaque and brown, with a range of colors seen in the transparent to translucent precious opal.

Tiger's eye is a golden brown, opaque variety of fibrous quartz that is valued for its chatoyancy (the cat's eye effect). This optical phenomenon is caused by parallel inclusions that reflect rays of light. In order to best display this, tiger's eye gemstones are often given a cabochon cut. Tiger's eye is related to hawk's eye and pietersite, and is commercially mined in several areas of the world, though currently, the most important tiger's eye deposits are South Africa and Thailand.

Tiger's eye matrix is tiger's eye which is cut and finished with some of the matrix (host rock) intact. When tiger's eye, red jasper and black hematite are all present, it is traded as "tiger's iron". Depending on composition, tiger's eye matrix gemstones can show the whole range of golden tiger's eye, gray to black hematite and red jasper colors, in swirls or bold bands. Since tiger's eye matrix is an aggregate, its luster varies according to its content; hematite has a metallic luster, tiger's eye has a changeable luster and jasper has a dull to vitreous luster.

Scapolite is a rare gemstone that is mostly seen in gem and mineral collections. Scapolite gemstones occur in various colors, including yellow, violet, orange, pink, gray, colorless and brown. There are several varieties of scapolite, such as rainbow scapolite, which is colorless scapolite with multicolored inclusions and cat's eye scapolite, which has parallel-aligned inclusions causing light to be reflected in the shape of the slit eye of a cat. Cat's eye scapolite has nice, sharp cat's eyes and is often a rich brown color.

Tourmaline is a boron silicate mineral that occurs in every color of the rainbow, including brown. One of the fascinating phenomena of brown tourmaline gemstones is their pleochroism; the ability to exhibit different colors depending on the viewing angle. This results in interesting multicolor tourmaline gemstones that may be brown, yellow and green all in one stone. Brown tourmaline has a Mohs hardness of 7-7.5 and a vitreous luster. Trade names for brown tourmaline include "dravite" and "tsilaisite".

Andalusite is a lesser-known gem that gets its name from Andalusia, where it was first found, though it is now found in many places, such as Australia, Russia, Canada, Brazil, Sri Lanka and the USA. It shares the same composition as sillimanite and kyanite (aluminum silicate), making all three minerals polymorphs; minerals with the same composition, but different crystal structures. Andalusite has strong pleochroism; the ability to exhibit different colors from different angles, which gives andalusite unique combinations of color.

Axinite is a rare, violet, blue or brown gem type composed of calcium borate silicate which is a popular collector's stone. Its name comes from a Greek word for "axe" because of its unusual, spatula-shaped crystals. Interesting phenomena of axinite include its pyro- and piezoelectric properties, meaning that it can generate an electric current when heated, cooled or exposed to mechanical stress or pressure.

Cassiterite is a the primary ore for tin and a rare collector's gemstone composed of tin oxide that is sometimes called the "tin stone". The name, "cassiterite" comes from a Greek word meaning "tin". Cassiterite gemstones may be brown or black and have an extremely high refractive index, giving them remarkable fire and dispersion, as well as an attractive adamantine or submetallic luster. Though cassiterite is mostly a collector's stone, it is hard enough to be used for jewelry.

Color change garnet is one of the rare varieties of garnet gemstones and can be many different colors, including green, pink, peach, bluish, purple, reddish or brown. Color change garnet gemstones are typically a mix of spessartite and pyrope garnet and tend to shift to a warmer color under incandescent light. The most frequently seen colors in color change garnet are brownish-green or bronze under daylight and rose or pink under incandescent light, though some stones may be other color combinations.

Diamond is composed of pure carbon and is the hardest material on earth, with a Mohs hardness rating of 10. Brown diamonds are a fancy diamond color that was not popular until relatively recently. The incredible hardness, brilliance and adamantine luster of diamond, along with clever marketing techniques for "chocolate" and "cognac" diamonds, made brown diamonds a hit. Colored diamond gemstones are graded by color intensity, with the highest saturation of color being the rarest and most valuable.

Enstatite is a pyroxene mineral that is rarely found in gemstone quality. Its name comes from the Greek for "resistor", due to its high melting point. Fine enstatite is transparent and may be greenish-brown, yellowish, green, brown or colorless. Golden brown enstatite is colored by traces of iron. Since enstatite is relatively soft, it is mostly used as a collector's gemstone, or reserved for pendants and earrings.

Golden beryl is a yellow to honey-colored member of the beryl family; the same group of gemstones as morganite, emerald and aquamarine. Though golden beryl is the most affordable and easily available beryl gemstone, it is lesser known than its more famous cousins. Golden beryl is also known as "precious beryl" and pale golden beryl stones are sometimes referred to as "heliodor", which comes from the Greek for "gift of the sun".

Hessonite is a honey-yellow, orange or reddish-brown grossular garnet variety that is also known as "cinnamon stone" or "kaneel stone" because of its brown-red color, which comes from traces of manganese. Hessonite garnet is an important Vedic astrology stone and also a January birthstone. Typically a heavily-included stone, hessonite is generally transparent to translucent with a vitreous luster. Hessonite has a remarkably high refractive index, giving it exceptional brilliance. It is found in various locations, but the most famous source for hessonite garnet is Sri Lanka.

Jasper is a type of opaque chalcedony that is assigned its own gem group because it has a grainy structure that differs from typical chalcedony. The name "jasper" comes from the Greek for "spotted stone" with reference to its multicolored spots, stripes and other patterns. The variegated appearance of jasper is owed to the fact that it is composed of up to twenty percent foreign materials. This means that each jasper gemstone is quite unique and there is an almost infinite variety of colors and patterns. Trade names for jasper incude "Zebra jasper"; which refers to dark-brown jasper with zebra-like bands.

Kornerupine is a rare magnesium aluminum borosilicate gemstone named after Danish naturalist, artist and explorer, Nikolaus Korneup. Despite being known since 1887, kornerupine remains a lesser-known gemstone. Kornerupine gems may be brown, brownish-green, green, white, pink, yellow or blue and are also sometimes traded as "prismatine", in reference to their long, prismatic crystal structure. Pronounced pleochroism is an interesting property of kornerupine, which can display yellow, green and brown in a single gemstone, depending on the viewing angle.

Mali garnet is a rare "hybrid" grossular garnet variety from Mali in West Africa that was discovered in 1994, making it a relatively recent addition to the garnet gemstone group. The colors of Mali garnet range from yellow to brown, with the most valued stones being green. Its remarkable dispersion and high refractive index give Mali garnet wonderful fire and brilliance, which is showcased by facet cuts. Mali garnet gems are transparent to opaque and have a Mohs hardness of 7.

Obsidian is natural volcanic glass that forms as lava cools and can take various forms and colors, depending on the composition of the lava. For example, "mahogany obsidian" has reddish-brown streaks running through it and "gold sheen", as the name suggests, has a golden, glittery sheen. In its pure form, obsidian has a dark body color, due to the presence of iron and magnesium. Obsidian is transparent to opaque with a vitreous luster and has been used as a gemstone for many years. Obsidian gemstones are often made into cabochons, carvings or cut into spheres.

Pietersite is a rare dark-gray, midnight-blue, reddish or brown aggregate that is composed of mostly hawk's eye and tiger's eye (crocodilite). The crocodilite of pietersite appears as chatoyant (light-reflecting) swirls or streaks. When pietersite has more tiger's eye content, it results in a brown pietersite gemstone. To showcase their chatoyancy, pietersite gemstones are cut as cabochons.

Rutile quartz is transparent quartz that contains rutile (titanium dioxide) inclusions in the form of needles, which may be black, green, red or brown and make an internal landscape inside the gem. When the rutile inclusions are dense, the color of the gemstone appears to take on the color of the inclusions. Thus, rutile quartz stones that contain dense, brown rutile inclusions look brown. These intriguing but affordable gemstones are cut in many different shapes and styles.

Sillimanite is made of the same polymorphic material as both andalusite and kyanite; aluminum silicate. Though these three gemstones share the same composition, their crystal structures differ. Transparent sillimanite is rarely found, but is typically greenish to yellow in color, with the occasional light-blue or violet-brown stone. Cat's eye sillimanite is usually brown, though it can also be violet. Sillimanite is the official state mineral of Delaware, though it was originally found in Connecticut.

Sphalerite is composed of zinc ore and has very high dispersion, giving it incredible "fire", as well as fiery yellow, orange, red and brown colors. Its resinous to adamantine luster also adds to sphalerite's attraction. Since sphalerite lacks hardness, it is mainly a collector's stone. Sphalerite is found in several locations, including Bulgaria, Canada, Spain, the Congo, Namibia, the USA and Zaire, however, it is rarely found in gemstone quality.

Agate is a banded form of chalcedony quartz that occurs in many different colors and even geodes, which are rock cavities or vugs with internal crystal formations or concentric banding. Brown agate gemstones include fire agate, which is admired for its fiery iridescence; and dendritic agate; brown agate with black dendritic inclusions. Agate gems are extremely versatile and may be sold as beads, cabochons, faceted gems, agate geodes, carvings, slices or as tumbled stones. Agate geode gems and slices are particularly popular for their "raw" look. Jewelry made from agate is hard and durable enough to last for centuries, with a pleasing waxy luster and translucent to opaque clarity.