Danburite is known for its distinct, well formed, and often gemmy crystals. Danburite... More
Danburite is known for its distinct, well-formed, and often gemmy crystals. Danburite crystals are sometimes coated or entirely encrusted with drusy Quartz, and the Quartz may occasionally form a pseudomorph, completely replacing the Danburite. Danburite is named after the city of Danbury, Connecticut, where this mineral was first described. It was first discovered as a distinct species in 1839 by Charles Shepard, in an undocumented and presumably built-over location within the city. For additional information, see the gemstone section on Danburite. Hide
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Datolite forms in very attractive crystals that can be highly lustrous and very spark... More
Datolite forms in very attractive crystals that can be highly lustrous and very sparkly, or have frosted crystal faces. A totally different form of Datolite are the oval-shaped nodules that lack any distinctive crystal form. These nodules can be sliced and polished to show beautiful coloring and patterns within the nodule. Nodules are often colored by Copper inclusions which can give them a reddish color.
Datolite was named in 1806 by Jens Esmark, a Danish-Norwegian professor of mineralogy, for the Greek term " dateishai", which means to divide, alluding to the often grainy aggregates of Datolite which break easily.
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Diamond has many unequaled qualities and is very unique among minerals. It is the har... More
Diamond has many unequaled qualities and is very unique among minerals. It is the hardest known substance, it is the greatest conductor of heat, it has the highest melting point of any substance (7362° F or 4090° C), and it has the highest refractive index of any natural mineral. Diamond is number 10 on the Mohs scale, and is approximately 4 times harder than Corundum, which is number 9 on the Moh's scale. It also has the most dense atomical configuration of any mineral, and is transparent over the greatest number of wavelengths. Because of heat conduction, Diamonds are cold to the feel at or below room temperature. When heated, a Diamond will remain hot long after the heat source is removed. The luster of Diamond is excellent. Diamond exhibits great " fire" and brilliance, which gives it a shiny, freshly polished look. Rough Diamonds exhibit a greasy luster, but proper cutting give them a powerful adamantine luster. Only synthetic substances and a few minor gemstones can reach or excel the refractive index of Diamonds. The hardness and refractive index may slightly vary among Diamond specimens. Bort and Carbonado exhibit a slightly lower hardness than other Diamonds, and lack cleavage. Lonsdaleite (also known as Hexagonal Diamond), is a type of Diamond found with meteorites and is of extraterrestrial origin. It is scientifically a different mineral than Diamond, and believed to have formed when meteoric Graphite fell to earth. When this happened, great heat and stress transformed the Graphite into Diamond, but it retained Graphite's hexagonal crystal lattice. For additional information, see the gemstone section on Diamond. Hide
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Diaspore is one of the three component minerals of the economically important aluminu... More
Diaspore is one of the three component minerals of the economically important aluminum ore Bauxite. Though most forms of this mineral are not of much interest to the collector, large exceptional crystals unlike any others were found in Turkey in the 1950's in a commercial Bauxite deposit. This deposit has become the source of mining operations producing exceptional specimens and gem-grade crystals that are cut into gemstones. The company operating the gem Diaspore mine was previously called Zultanite Gems LLC, and they had given this form of Diaspore the trade name " Zultanite". They have recently dropped this name in favor of a new trade name, Csarite. For additional information, see the gemstone section on Diaspore. Hide
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Diopside is a very common mineral and forms as an accessory mineral in many environme... More
Diopside is a very common mineral and forms as an accessory mineral in many environments, and is an important constituent of skarn rocks. Diopside forms a series with Hedenbergite, the iron equivalent of Diopside, and may be partially replaced by it. In fact, Diopside and Hedenbergite can even occur together in a single crystal, with a core of Hedenbergite and outer zone of Diopside. Diopside almost always contains a slight amount of iron replacement, and pure, iron-free Diopside is rather uncommon. Additional iron in the chemical structure of Diopside will cause a darker color and decreased transparency. For additional information, see the gemstone section on Diopside. Hide
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Dioptase is a brightly colored mineral, highly desired for its intense green color. I... More
Dioptase is a brightly colored mineral, highly desired for its intense green color. It can form in very distinctive, well-developed crystals, but only a handful of well-known deposits have produced large crystals. Most localities of this mineral, including those in Arizona, only produce microcrystals. Dioptase crystals are generally fragile and can easily break or crumble, and therefore care must be exercised when handling specimens. Dioptase was named in 1797. Its name is derived from a combination of the Greek words Dia, which means "through" and Optasia, which means "to see". This is regarding the ability to see internal cleavage planes within transparent to translucent crystals of Dioptase. Hide
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Dolomite is a very common mineral, and is known for its saddle shaped curved crystal ... More
Dolomite is a very common mineral, and is known for its saddle-shaped curved crystal aggregates. A unique, isolated Dolomite occurrence in Eugui, Spain has provided
colorless transparent crystals that resemble the Iceland Spar
variety of Calcite. The occurrence of Kolwezi, in the Congo, has produced some fascinating, cobalt-rich specimens that are a beautiful hot pink color and highly popular. Dolomite forms in a different crystal class, differing from the Calcite group minerals. This can be noted by the fact that Dolomite generally forms more elongated crystals than those of the Calcite group. In addition, Dolomite never occurs in scalenohedral crystals, whereas minerals of the Calcite group do. Dolomite is used to describe both a mineral and a rock. The mineral is the pure form with a defined crystal structure and chemical formula, whereas dolomite rock is composed chiefly of the mineral Dolomite, but also contains impurities such as Calcite, Quartz, and feldspar. Hide
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Dravite is best known as the Brown Tourmaline . It is a relatively common form of Tou... More
Dravite is best known as the "Brown Tourmaline". It is a relatively common form of Tourmaline, and often forms in crude uninteresting formation. However, crystals from certain localities can be highly lustrous and beautifully crystallized. Dravite is named after Dravograd, in Slovenia, the area where Dravite was first described. Dravite may be partially replaced or intergrown together with Schorl, with a specimen being part Dravite and part Schorl. Dravite is also very similar to Uvite and Fluor-uvite, and may occur together with Uvite/Fluor-uvite in a single crystal. It can sometimes be very difficult to make an exact distinction between Dravite and Uvite/Fluor-uvite. Hide
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div Dumortierite often forms in an attractive blue color and can be used as an orname... More
Dumortierite often forms in an attractive blue color and can be used as an ornamental stone. Though it is most commonly perceived as blue, especially in lapidary use, other colors include purple, pink, gray and brown. Dumortierite specimens are composed of dense fibers, giving them a tough durability.
Dumortierite often forms as inclusions in Quartz, and this combination results in a natural blue Quartz gemstone. These are known in the gemstone market as " Dumortierite Quartz" and they are becoming increasingly popular as a minor blue gemstone. Dumortierite is named after French paleontologist Eugene Dumortier (1803-1873).
For additional information, see the gemstone section on Dumortierite.
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