Crocoite
Crocoite is a rare lead chromate mineral and very rare being a gem that is faceted. It is certainly one of only 25 chromate minerals, most of which are rare. It’s very soft with a Moh’s hardness of just 2.5-3.0 and features a very high dispersion, but this is masked by the colour that is intense. Crocoite’s intense colour that is reddish-orange almost unique in the treasure globe and makes this really uncommon gem even more desirable. Its density is extremely high at 5.9-6.1 due to its lead (Pb) content of about 64 chromium and%(Cr) content of about 16%. This density that is high Crocoite among the list of densest of all of the translucent minerals. Because of its thickness, Crocoite has an index that is unusually high of 2.31-2.66, which approximates compared to Diamond (2.417). Crocoite is connected with other lead that is secondary Pb) minerals such as for example Cerussite, Pyromorphite, Vanadinite, Wulfenite and a number of rare chromates.
The mineralogist that is german Gottlob Lehmann (1719-1767) identified orange-red specimens through the type locality during the Tsvetnoi Mine near Sverdlowsk, Russia, as a new mineral in 1763. He called it “red-lead ore” which became referred to as “red lead of Siberia” and later on “Siberian red lead.” In 1770, German scientist Peter Simon Pallas (1741-1811) ground specimens from the same site into a bright yellow powder that he found useful as a paint pigment and fabric dye which quickly gained popularity throughout Russia and European countries.
Siberian lead that is red proven to include lead but the remainder of its chemical composition stayed a mystery until 1797, whenever French chemist Louis Nicolas Vauquelin (1763-1829) addressed samples of Siberian red lead with acid to produce an oxide that included a previously undiscovered element; a hard, lustrous, steel-gray metal with a high melting point and a thickness just like that of iron. Vauquelin named this element that is new chromium” after the Greek word chrōma, meaning color, in allusion to the bright colors of its salts (compounds). Vauquelin credited both R.J. Haüy and A.F. de Fourcroy with the suggested name.
Since its discovery, Crocoite has been provided names that are many synonyms from many sources. The following is a list of a lot of its names, along with their sources and dates.
Nova minera Plumbi; J.G. Lehmann, 1766
Plomb rouge; B.G. Sage, 1769
Minerai de plomb rouge; P.S. Pallas, 1770
Plumbum hexaedrum rhombeum fulvum; Rome de Itsle, 1772
Rotbleierz (or Rothes Bleierz); A.G. Werner, 1774
Minera plumbi rubra; J.G. Wallerius, 1775
Minera plumbi spathosa; B.F.J. Hermann, 1789
Plombe rouge de Sibérie; L. Macquart, 1789
Plomb chromaté; R.J. Haüy, 1801
Kallochrom; J.F.L. Hausmann, 1813
Crocoise; F.S. Beudant, 1832
Krokoisit; Fr. Von Kobell, 1838
Bleiischer Chromspath; A. Breithaupt, 1841
Beresofite; C.U. Shepard, 1844
Lehmannite; H.J. Brooke and W.H. Miller, 1852
A reference towards the distinct color of its powder in 1832 French mineralogist François-Sulpice Beaudant (1787-1850) gave “red lead ore” its first formal mineral name, “Crocoise,” from the Greek term krokos, meaning saffron. This name was later on changed to “Crocoisite” and eventually to the title that is presentCrocoite.” Saffron is just a spice derived from the flower of the Crocus sativus plant, popularly known as the saffron crocus. Saffron crocus bears up to four plants, each with three crimson that is vivid, that are dried out and used as a seasoning and coloring agent in meals.
The main and best known source for exceptional specimens is the Adelaide as well as other mines of the Dundas region, Tasmania, Australia. Crocoite was present in Tasmania in about 1886, and from the time has been the absolute most important source of Crocoite specimens and gemmy crystals of this mineral that is very sought-after. According to the well-known amateur that is tasmanian William Frederick Petterd (1849-1910) wrote: “The first discovery of the mineral had been made by Smith and Bell at the Heazlewood silver-lead mine. It occurs there in bright, shining hyacinth-red crystals, little from other portions of the island, arranged in acicular bunches, penetrating and attached to a really friable clayey gossan, intermixed by having a small cerussite, and more seldom pyromorphite. once we now know them” By the time mineralogists positively identified the mineral that is orange-red Crocoite in 1895, it had been found in mines of the nearby Luina, Waratah, Whyte River, and Zeehan districts. In 2000, the Honorable John Bestwick, minister of mines of the Australian State of Tasmania, declared Crocoite to be Tasmania’s mineral that is official.
Distribution: From the Tsvetnoi mine, Mt. Uspenskaya, the Preobrazhensky mine, and other mines, Beresovsk region, and on Mt. Tochil’naya, Center Ural Mountains, near Yekaterinburg (Sverdlovsk), Russia. At Băiţa Mining District (Baita Bihor; Rézbánya), Romania. In Germany, fine examples from Obercallenberg, near Glauchau, Saxony. Into the vein that is hopeful Leadhills, Lanarkshire, Scotland. From the Greystone quarry, Lezant, Cornwall, England. At the Cantonniers mine, Nontron, Dordogne, France. From Howard’s Luck mine, Umtali, and at a number of other occurrences being minor Zimbabwe. From the pb–Zn that is argent, about 100 km eastern of Johannesburg, Transvaal, South Africa. In Australia, as exceptional specimens as well as an ore of lead into the Dundas district, at the Adelaide, West Comet, as well as other mines, additionally from the Heazlewood, Whyte River, and Magnet mines, Tasmania; from the Happy Jack mine, Comet Vale, and other places in Western Australia; during the Wadnaminga gold mines, near Olary, South Australia. From Labo, Luzon, Philippines. At Goyabeira, near Congonhas do Campo, Minas Gerais, Brazil. Into the USA, from Darwin, Inyo County, Ca; during the Moon Anchor, Potter-Kramer, Pack Rat, and other mines south of Wickenburg, Maricopa County, Arizona.
| Category: | Chromate minerals |
| Chemical Formula: | PbCrO4 |
| Lead Chromate | |
| Molecular Weight: | 323.19 gm |
| Composition: | Chromium | 16.09 % | Cr | 30.94 % | CrO |
| Lead | 64.11 % | Pb | 69.06 % | PbO | |
| Oxygen | 19.80 % | O | |||
| 100.00 % | 100.00 % | = TOTAL OXIDE |
| Crystallography: | Monoclinic – Prismatic |
| Crystal Habit: | As prismatic to acicular crystals with the nearly square outline, elongated and striated [001], to 15 cm.; short prismatic to pseudo-octahedral, may be highly modified, terminations are commonly hollow or incomplete. Typically in radial sprays to randomly intergrown aggregates. |
| Twinning: | None |
| Cleavage: | Distinct on {110}; indistinct on {001} and {100} |
| Fracture: | Conchoidal |
| Tenacity: | Sectile |
| Moh’s Hardness: | 2.5 – 3.0 |
| Density: | 5.90 – 6.10 (g/cm3) |
| Luminescence: | None |
| Radioactivity: | Not Radioactive |
| Health Warning: | Contains lead – always wash hands after handling. Avoid inhaling dust when handling or breaking. Never lick or ingest. Avoid prolonged exposure in proximity to the body. Store away from inhabited areas. |
| Color: | Hyacinth-red, red-orange, orange; red-orange in transmitted light |
| Transparency: | Transparent to translucent |
| Luster: | Adamantine to vitreous |
| Refractive Index: | 2.290 – 2.660 Biaxial ( + ) |
| Birefringence: | 0.370 (very high) |
| Dispersion: | Very strong; r > v, inclined |
| Pleochroism: | Weak; X = Y = red-orange; Z = blood red |
