Rammelsbergite belongs to the Loellingite group, which is a group of chemically relat... More
Rammelsbergite belongs to the Loellingite group, which is a group of chemically related isomorphous minerals that are all rare. Other members discussed in this guide are Loellingite and Safflorite. Rammelsbergite was named after the German scientist K.F. Rammelsberg (1812-1899). Hide
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Raspite is a rare dimorph of the mineral Stolzite . In its most prolific locality of ... More
Raspite is a rare dimorph of the mineral Stolzite. In its most prolific locality of Broken Hill, Australia, Raspite almost always occurs together with Stolzite, with the Raspite more deeply colored and elongated than the Stolzite. Raspite is named after Charles Rasp (1846-1907). Rasp was credited for discovering the famous Broken Hill deposit, which is the type locality for this mineral and has produced its best examples. Hide
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span id ctl00 ContentPlaceHolder1 lblMineralDefinition style font family Verdana font... More
Realgar is an historically important mineral, with a striking ruby-red color that stands out in the mineral kingdom. The rare transparent lustrous forms are truly masterpieces in mineral aesthetics.
Realgar is a photosensitive mineral and will alter to Pararealgar upon prolonged exposure to light. Pararealgar is unstable and will eventually crumble into a yellow powder if left in the light. The alteration mineral that Realgar transformed into was generally assumed to be Orpiment, but recent scientific analysis has in fact determined the orange alteration product as Pararealgar. Due to the instability of Realgar, specimens should be stored enclosed and covered to prevent their exposure to light. Occasional exposure to look at a specimen will not cause damage; only prolonged or repeated exposure will cause alteration. Several important museums have had Realgar on display consistently exposed to light, and these specimens can be seen altered and crumbled.
Realgar contains a significant amount of poisonous arsenic, and is itself somewhat toxic. Washing hands is recommended after handling Realgar specimens, especially if they are powdery. Hide
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Rheniite is the only known mineral with the extremely rare element rhenium as its pri... More
Rheniite is the only known mineral with the extremely rare element rhenium as its primary metallic constituent, and as such is a fascinating and exotic species. However, Rheniite is too rare to be mined as an ore of rhenium. All rhenium is extracted from Molybdenite, which contains traces of rhenium in certain localities. Rheniite is named after its rhenium content, and rhenium is named after the Rhine River in Europe. Rheniite is a relatively new mineral, and was only accepted as an individual mineral species in 2004. Hide
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Rhodochrosite is a very aesthetic and desirable mineral its deep red and hot pink cry... More
Rhodochrosite is a very aesthetic and desirable mineral; its deep red and hot pink crystals are highly sought after. Of special note are the beautiful, intensely colored rhombohedral crystals that have come from the Sweet Home Mine in Colorado. This mine provided a fascinating discovery in the 1960's of some of the largest and most stunning Rhodochrosite crystals ever found. The largest Rhodochrosite crystal, called the "Alma King", is a single 15 cm crystal that was found in the Sweet Home Mine in 1992.
South Africa and Peru also produce intense red transparent scalenohedral crystals
that are also highly desirable to collectors. Some consider these Rhodochrosites, with the deep color, transparency, and well-formed crystals, to be the most beautiful of
all minerals. An interesting occurrence of this mineral is in Argentina, where
Rhodochrosite forms stalagmites and stalactites in the 13th century Inca Silver mines. They formed from precipitating water dripping from the manganese-rich rock inside the ancient mine tunnels, and kept on growing over the centuries into large stalagmites. These stalagmites are beautifully banded with concentric growth layer, and are often sliced and polished into slabs for collectors, and may be cut and polished for jewelry. Rhodochrosite belongs to the calcite group of minerals, a group of related carbonates that are isomorphous with one another. They are similar in many physical properties, and may partially or fully replace one another, forming a solid solution series. All members of the calcite group crystallize in the trigonal system, have perfect rhombohedral cleavage, and exhibit strong double refraction. When Rhodochrosite is exposed to the atmosphere, it may develop a thin film of manganese oxide on its surface. This may slightly darken the color of a specimen. Rhodochrosite sometimes alters into black manganese oxides (such as Pyrolusite, Manganite, and Psilomelane), and black manganese oxide stains are usually associated with Rhodochrosite. For additional information, see the gemstone section on Rhodochrosite. Hide
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Rhodonite is well known among collectors for its beautiful pink and red color. The re... More
Rhodonite is well known among collectors for its beautiful pink and red color. The red variety can be so deep red that it rivals the color of Ruby. The large crystals once found in Franklin, New Jersey, are classic rarities that make magnificent reference pieces. Rhodonite often has black manganese oxide veins running through a specimen, giving it the distinct appearance of pink with black crisscrossing lines and flower-like formations throughout. These are the forms most commonly used as gemstones, especially in beads and ornamental objects. Large massive specimens of black-streaked Rhodonite is often sliced and polished into slabs for collectors. For additional information, see the gemstone section on Rhodonite. Hide
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Riebeckite forms in two very different habits. The darker colored forms which are ind... More
Riebeckite forms in two very different habits. The darker-colored forms which are individually crystallized are generally of igneous origin, such as
volcanic rock and pegmatites. The finely fibrous variety, known as Crocidolite, usually originates from altered
metamorphic rocks. The Crocidolite variety is a type
of asbestos, and is sometimes also referred to as "blue asbestos". It is
considered to be the most hazardous form of asbestos, and should never be brought near the mouth. If its fibers or particles enter the lungs, they can cause asbestosis. Asbestosis is a lung disease caused by inhalation of asbestos particles, which causes several cancers, particularly lung cancer and mesothelioma. Symptoms of asbestosis do not arise until about 20 years after the inhalation. Due to the hazards, washing hands after handling specimens is highly recommended. Many mineral collectors avoid collecting asbestos minerals out of safety concerns. Riebeckite forms a series with Magnesio-riebeckite, which is the magnesium-dominated end member which has magnesium replacing part of the iron in its structure. Riebeckite crystals are frequently included within larger crystals of Quartz, and will sometimes turn the Quartz a blue color if the inclusions are very fine. Riebeckite was named after the German explorer and mineralogist Emil Riebeck (1853–1885). Tiger's Eye, a well-known inexpensive gemstone, is a pseudomorph of compact Quartz after finely the fibrous Crocidolite variety of Riebeckite. It is formed when the Quartz takes over and dissolves the Crocodolite, leaving the Quartz compact yet composed of solid fibrous - and chatoyant forms. When polished, it's silky luster creates a beautiful chatoyant effect of moving layers of brown and yellow lines and waves. Hide
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div Romanechite is sometimes synonymous with Psilomelane , but in reality Romanechite... More
Romanechite is sometimes synonymous with Psilomelane, but in reality Romanechite is a strictly defined mineral that is recognized by the IMA, whereas Psilomelane is not specifically identified, or is a compound of several barium manganse oxides including Romanechite. Romanechite is named after the locality of Romanèche-Thorens in France, the type locality for this mineral.
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Rutile comes in a surprising contrast of distinct habits and colors, making it a very... More
Rutile comes in a surprising contrast of distinct habits and colors, making it a very interesting mineral. It has multiple unique crystal forms as well as several telltale colors, styles, and associations. Rutile can range from mirror-like metallic-looking crystals, to dark reddish sub-metallic crystals, to bright golden-yellow needles. Even the opaque metallic-looking forms are somewhat translucent on edge under backlighting, with a dark red translucent tinge. Rutile is well known for its habit of forming needle-like inclusions within other minerals, especially Quartz, in the form of long and slender yellow straw-like crystals. These inclusions can range from scattered needles to dense parallel fibers within a host mineral. This combination is known as Rutilated Quartz, and is used both as a collectors mineral and gemstone. Rutile inclusions are also responsible for the asterism or chatoyancy effects on some gemstones, such as Star Sapphire. The thin, parallel Rutile fibers that formed within the host mineral provide these unique optical effects. Rutile is the most common mineral composed of titanium dioxide. Rarer polymorphs include Brookite and Anatase, both which also form unique and distinctive crystals. The name Rutile is derived from the Latin "Rutilus", in reference to a common color habit of this mineral in dark red but lustrous crystals.
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