Crocoite
Current inventory: 1 gem
 

  
Crocoite is named from the Greek word krokos, meaning saffron, in allusion to its distinctive saffron-orange color.

Discovered in 1763; IMA status: Valid (pre-IMA; Grandfathered)

Chemistry

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

Classification

Mineral Classification:

Sulfates

Strunz 8th Ed. ID:

6/F.01-30

Nickel-Strunz 10th Ed. ID:

7.FA.20

7 : SULFATES (selenates, tellurates, chromates, molybdates, wolframates)
F : Chromates
A : Without additional anions

Related to:

n/a

Varieties:

None

Synonyms:

Beresofite (of Shepard), Beresowite (of Shepard), Callochrome, Chromate of lead, Crocoisite, Kollochrom, Lehmannite, Red lead ore

Crystal Data

Crystallography:

Monoclinic - Prismatic

Crystal Habit:

As prismatic to acicular crystals with 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

Physical Properties

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 of the body. Store away from inhabited areas.

Optical Properties

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

Occurances

Geological Setting:

An uncommon secondary mineral in the oxidized portions of lead deposits associated with chromium-bearing rocks; may be of post-mine formation.

Common Associations:

Phoenicochroite, Vauquelinite, Embreyite, Pyromorphite, Dundasite, Vanadinite, Descloizite, Wulfenite, Cerussite, Anglesite, Quartz, “limonite”

Common Impurities:

Zn, S

Type Locality:

Tsvetnoi Mine, Uspenskaya Mt, Berezovskoe Au Deposit (Berezovsk Mines), Berezovskii (Berezovskii Zavod), Ekaterinburg (Sverdlovsk), Sverdlovskaya Oblast', Middle Urals, Urals Region, Russia

Year Discovered:

1763

View mineral photos:

Crocoite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Crocoite is a rare lead chromate mineral and very rare as a faceted gem. It is one of only 25 chromate minerals, all of which are rare. It is very soft with a Moh's hardness of only 2.5-3.0 and has a very high dispersion, but this is masked by the intense color. Crocoite's intense reddish-orange color is almost unique in the gem world and makes this very rare gem even more desirable. Its density is extremely high at 5.9-6.1 due to its lead (Pb) content of about 64% and chromium (Cr) content of about 16%. This high density makes Crocoite among the densest of all translucent minerals. Because of its density, Crocoite has an unusually high index of refraction of 2.31-2.66, which approximates that of Diamond (2.417). Crocoite is associated with other secondary lead (Pb) minerals such as Cerussite, Pyromorphite, Vanadinite, Wulfenite and a number of rare chromates.

The German mineralogist Johann Gottlob Lehmann (1719-1767) identified orange-red specimens from the type locality at the Tsvetnoi Mine near Sverdlowsk, Russia, as a new mineral in 1763. He called it "red-lead ore" which became known as "red lead of Siberia" and later "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 Europe.

Siberian red lead was known to contain lead but the remainder of its chemical composition remained a mystery until 1797, when French chemist Louis Nicolas Vauquelin (1763-1829) treated samples of Siberian red lead with acid to produce an oxide that contained a previously undiscovered element; a hard, lustrous, steel-gray metal with a high melting point and a density similar to that of iron. Vauquelin named this new element "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 given many names and synonyms from many sources. The following is a list of many 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

In 1832 French mineralogist François-Sulpice Beaudant (1787-1850) gave "red lead ore" its first formal mineral name, "Crocoise," from the Greek word krokos, meaning saffron, a reference to the distinct color of its powder. This name was later changed to "Crocoisite" and eventually to the present name "Crocoite." Saffron is a spice derived from the flower of the Crocus sativus plant, commonly known as the saffron crocus. Saffron crocus bears up to four flowers, each with three vivid crimson stigmas, which are dried and used as a seasoning and coloring agent in food.

The main, and best known source for exceptional specimens is the Adelaide and other mines of the Dundas district, Tasmania, Australia. Crocoite was found in Tasmania in about 1886, and ever since has been the most important source of Crocoite specimens and gemmy crystals of this highly sought-after mineral. According to the well-known Tasmanian amateur mineralogist William Frederick Petterd (1849-1910) wrote: “The first discovery of the mineral was made by Smith and Bell at the Heazlewood silver-lead mine. It occurs there in bright, shining hyacinth-red crystals, small as we now know them from other portions of the island, arranged in acicular bunches, penetrating and attached to a very friable clayey gossan, intermixed with a little cerussite, and more rarely pyromorphite.” By the time mineralogists positively identified the orange-red mineral as Crocoite in 1895, it had also 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 official mineral.

Distribution: From the Tsvetnoi mine, Mt. Uspenskaya, the Preobrazhensky mine, and other mines, Beresovsk district, and on Mt. Tochil’naya, Middle Ural Mountains, near Yekaterinburg (Sverdlovsk), Russia. At Băiţa Mining District (Baita Bihor; Rézbánya), Romania. In Germany, fine examples from Obercallenberg, near Glauchau, Saxony. In the Hopeful vein, 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 minor occurrences in Zimbabwe. From the Argent Pb–Zn mines, about 100 km east of Johannesburg, Transvaal, South Africa. In Australia, as exceptional specimens and an ore of lead in the Dundas district, at the Adelaide, West Comet, and other mines, also from the Heazlewood, Whyte River, and Magnet mines, Tasmania; from the Happy Jack mine, Comet Vale, and several other places in Western Australia; at the Wadnaminga gold mines, near Olary, South Australia. From Labo, Luzon, Philippines. At Goyabeira, near Congonhas do Campo, Minas Gerais, Brazil. In the USA, from Darwin, Inyo County, California; at the Moon Anchor, Potter-Kramer, Pack Rat, and other mines south of Wickenburg, Maricopa County, Arizona.
 

  
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