Herderite

Trolleite Quartz is a rare variety of quartz known for its unique blue-green coloration, caused by inclusions of the mineral Trolleite. It is named after the Swedish chemist and mineralogist Hans Gabriel Trolle-Wachtmeister, who discovered it in the 19th century. Initially, trolleite Quartz was thought to be exclusive to Sweden's Vastana mine, making it an exceptionally rare gemstone. However, further exploration led to the discovery of additional sources, expanding its availability to some extent. Presently, one of the prominent locations for trolleite Quartz mining is the Minas Gerais region in Brazil.

Lazulite is a deep blue mineral that is often confused for the more famous (and also very blue) lapis lazuli. This rare stone, unlike the more amorphous lapis lazuli, has cleavage planes (essentially, angular faces along which the crystal may split). Lazulite is occasionally used to make jewelry – although only somewhat translucent in its native form, it can become relatively transparent when correctly cut.

Hausmannite is rich in magnesium and occasionally appears as a genuinely captivating gemstone. When processed through Ferro manganese refining, it creates a dark brown color for pavers and bricks. In nuclear applications, hausmannite is used to promote proton travel, but only when dissolved in water. Specimens are highly collectible and range wildly in price.

One of the most famous and widely-used substances in the world, coal is a dark-colored rock that is rich in carbon. It was formed from decaying plant and animal material, compressed under the earth over millions of years. Coal provided the heat and energy needed to spur the industrial era in the 1800s, though it is thought to have been used for household heating in China as far back as 3000 BC.

Cuprite, although varied in colors, is predominately made of copper. This beautiful stone has been excavated worldwide, with some of the largest collections found in the American Southwest's copper veins. It is heavily mined as an ore and used for creating industrial-strength copper products. It is also called "ruby copper" because of its reddish tinge.

Granulite is a common metamorphic rock, formed at very high temperatures, that is primarily composed of quartz and feldspar and often contains many tiny (non-gem-quality) garnets. Variable in color and pattern, often displaying some banding, and taking a polish well, granulite is used decoratively for countertops or flooring.

Creedite is a rare and striking mineral that comes in hues ranging from clear to purple to brownish-orange. The mineral is so-named because it was first discovered and described near the small town of Creede, Colorado. Though not particularly well-known, creedite can be prized by collectors, as it often forms handsome and colorful crystal clusters.

Uvarovite Garnet is a rare variety of garnet that usually bears a rich green color. Unfortunately, its crystals are usually too small to be faceted into gemstones, though pieces are sometimes incorporated into jewelry anyway. Found in scattered locations around the world, the most prominent source of uvarovite Garnet is a mine in central Finland.