Diaspore

The rarest variety of beryl, this mineral is so rare that only one red Beryl is mined for every 150,000 gem-quality diamonds. It is found only in the USA and big-sized stones are extremely difficult to mine. Also known as red emerald, red Beryl is extremely expensive due to its beauty and rarity.

The transparent crystals of ettringite are long and hexagonal, but they're rarely cut into gems as they are colorless and quite soft. This mineral is used to coat paper to create "satin white" finish, and is also an important hydration product of cement, created during the chemical reactions of the stiffening process.

The term "prase" refers to a translucent, leek-green type of quartz, most commonly quartzite, but also some true quartzes and jaspers of similar color. The term is no longer considered to have much scientific meaning, since it covers so many differing types of rocks. Stones of this beautiful color have been carved for decorative purposes since ancient Greece.

Mixite occurs in transparent and translucent blues and greens but may be colorless when placed in front of transmitted light. It has a hexagonal crystal system that gives a fibrous appearance. This rare secondary mineral can be found in oxidized copper-bismuth deposits. Mixite is named after Czech mining engineer, Anton Mixa.

Austinite is a rare mineral usually translucent or transparent white or green, but colorless when put up against transmitted light. This mineral may be found alongside metal deposits containing arsenic. Austinite should not be confused with Austenite, which is a form of iron.

Wurtzite is a reddish-brown mineral found in hydrothermal conditions that are rich in zinc as well as in some sedimentary rocks. Wurtzite is a dimorph of sphalerite, meaning that their composition is the same but the way they form crystals is different. Wurtzite was discovered in 1861 and is named after the French chemist, Charles Adolphe Wurtz.

Rutile is a fairly common mineral mined for its titanium, which has many industrial uses (perhaps most famously in airplanes and spacecraft). When powdered, it is also used to make a strong white pigment. Although rarely carved as a gemstone in its own right, long, thin rutile crystal inclusions in other stones can create beautiful patterns, making these crystals more sought after (contrary to the general rule, in which gemstones with inclusions are less valuable).

Enargite is an important ore of copper, but it also occurs with other minerals and chemical elements such as Quartz, Bornite, Pyrite, or even Gold. This very common mineral is found in deposits related to low temperatures. It mostly occurs as a distinct steel-gray to black crystal with a violet film, but sometimes it can be dull gray.