Crocoite

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Crocoite
Crocoite from the Dundas extended mine, Dundas, Tasmania, Australia.jpg
Crocoite from Dundas, Tasmania
General
Category Chromate minerals
Formula
(repeating unit)		Lead Chromate PbCrO4
IMA symbol Crc [1]
Strunz classification 7.FA.20
Crystal system Monoclinic
Crystal class Prismatic (2/m)
(same H-M symbol)
Space group P21/n
Unit cell a = 7.12 Å, b = 7.421 Å,
c = 6.8 Å; β = 102.41°; Z = 4
Identification
ColorOrange, red, yellow; orange-red in transmitted light.
Crystal habit Coarsely crystalline to acicular
Cleavage Distinct on {110} indistinct on {001} and {100}
Fracture Conchoidal to uneven
Tenacity Sectile
Mohs scale hardness2.5–3
Luster Adamantine, Sub-Adamantine, Sub-Vitreous, Resinous, Waxy
Streak Yellowish orange
Diaphaneity Transparent to translucent
Specific gravity 5.9–6.1
Optical propertiesBiaxial (+)
Refractive index nα = 2.290(2) nβ = 2.360(2) nγ = 2.660(2)
Birefringence δ = 0.370
Pleochroism Weak
References [2] [3] [4]

Crocoite is a mineral consisting of lead chromate, Pb Cr O 4, and crystallizing in the monoclinic crystal system. It is identical in composition with the artificial product chrome yellow used as a paint pigment. [5]

Contents

Description

Crocoite is commonly found as large, well-developed prismatic adamantine crystals, although in many cases are poorly terminated. Crystals are of a bright hyacinth-red color, translucent, and have an adamantine to vitreous lustre. On exposure to UV light some of the translucency and brilliancy is lost. The streak is orange-yellow; Mohs hardness is 2.5–3; and the specific gravity is 6.0.

Crocoite crystal structure Crocoite crystal structure.png
Crocoite crystal structure

It was discovered at the Berezovskoe Au Deposit (Berezovsk Mines) near Ekaterinburg in the Urals in 1766; [6] and named crocoise by F. S. Beudant in 1832, from the Greek κρόκος (krokos), [7] saffron, in allusion to its color, a name first altered to crocoisite and afterwards to crocoite. In the type locality the crystals are found in gold-bearing quartz-veins traversing granite or gneiss and associated with crocoite are quartz, embreyite, phoenicochroite and vauquelinite. Phoenicochroite is a basic lead chromate, Pb2CrO5 with dark red crystals, and vauquelinite a lead and copper phosphate-chromate, Pb2CuCrO4PO4OH, with brown or green monoclinic crystals. Vauquelinite was named after Louis Nicolas Vauquelin, who in 1797 discovered (simultaneously with and independently of M. H. Klaproth) the element chromium in crocoite. [5]

Abundant masses with exceptional examples of crocoite crystals have been found in the Extended Mine at Mount Dundas as well as the Adelaide, Red Lead, West Comet, Platt and a few other Mines at Dundas, Tasmania; they are usually found in long slender prisms, usually about 10–20 mm but rarely up to 100 mm (4 inches) in length, with a brilliant lustre and color. Crocoite is also the official Tasmanian mineral emblem. [8] Other localities which have yielded good crystallized specimens are Congonhas do Campo near Ouro Preto in Brazil, Luzon in the Philippines, Mutare in Mashonaland, [5] near Menzies in Western Australia, plus Brazil, Germany and South Africa.

The relative rarity of crocoite is connected with the specific conditions required for its formation: an oxidation zone of lead ore bed and presence of ultramafic rocks serving as the source of chromium (in chromite). Oxidation of Cr3+ into CrO42− (from chromite) and decomposition of galena (or other primary lead minerals) are required for crocoite formation. These conditions are relatively unusual.

As crocoite is composed of lead(II) chromate, it is toxic, containing both lead and hexavalent chromium. [9]

Crocoite from Tasmania has been mined from the Dundas Extended Mine by Mike and Eleanor Phelan since the mid-1980s, but the mine's origins date back to 1892 when it was used as a prospecting tunnel for silver lead. As at April 2019, the mine is for sale (A$300,000) with the owners then continuing to operate the nearby Stichtite mine. [10]

Examples of crocoite

See also

Related Research Articles

<span class="mw-page-title-main">Chromate and dichromate</span> Chromium(VI) anions

Chromate salts contain the chromate anion, CrO2−
4. Dichromate salts contain the dichromate anion, Cr
2O2−
7. They are oxyanions of chromium in the +6 oxidation state and are moderately strong oxidizing agents. In an aqueous solution, chromate and dichromate ions can be interconvertible.

<span class="mw-page-title-main">Epidote</span> Sorosilicate mineral

Epidote is a calcium aluminium iron sorosilicate mineral.

<span class="mw-page-title-main">Cerussite</span> Lead carbonate mineral

Cerussite (also known as lead carbonate or white lead ore) is a mineral consisting of lead carbonate (PbCO3), and is an important ore of lead. The name is from the Latin cerussa, white lead. Cerussa nativa was mentioned by Conrad Gessner in 1565, and in 1832 F. S. Beudant applied the name céruse to the mineral, whilst the present form, cerussite, is due to W. Haidinger (1845). Miners' names in early use were lead-spar and white-lead-ore.

<span class="mw-page-title-main">Wulfenite</span> Molybdate mineral

Wulfenite is a lead molybdate mineral with the formula PbMoO4. It can be most often found as thin tabular crystals with a bright orange-red to yellow-orange color, sometimes brown, although the color can be highly variable. In its yellow form it is sometimes called "yellow lead ore".

<span class="mw-page-title-main">Murdochite</span>

Murdochite is a mineral combining lead and copper oxides with the chemical formula PbCu
6O
8−x(Cl,Br)
2x (x ≤ 0.5).

<span class="mw-page-title-main">Mimetite</span> Lead arsenate chloride mineral

Mimetite is a lead arsenate chloride mineral (Pb5(AsO4)3Cl) which forms as a secondary mineral in lead deposits, usually by the oxidation of galena and arsenopyrite. The name derives from the Greek Μιμητής mimetes, meaning "imitator" and refers to mimetite's resemblance to the mineral pyromorphite. This resemblance is not coincidental, as mimetite forms a mineral series with pyromorphite (Pb5(PO4)3Cl) and with vanadinite (Pb5(VO4)3Cl). Notable occurrences are Mapimi, Durango, Mexico and Tsumeb, Namibia.

<span class="mw-page-title-main">Leadhillite</span> Lead sulfate carbonate hydroxide mineral

Leadhillite is a lead sulfate carbonate hydroxide mineral, often associated with anglesite. It has the formula Pb4SO4(CO3)2(OH)2. Leadhillite crystallises in the monoclinic system, but develops pseudo-hexagonal forms due to crystal twinning. It forms transparent to translucent variably coloured crystals with an adamantine lustre. It is quite soft with a Mohs hardness of 2.5 and a relatively high specific gravity of 6.26 to 6.55.

<span class="mw-page-title-main">Vauquelinite</span>

Vauquelinite is a complex mineral with the formula CuPb2(CrO4)(PO4)(OH) making it a combined chromate and phosphate of copper and lead. It forms a series with the arsenate mineral fornacite.

<span class="mw-page-title-main">Phoenicochroite</span>

Phoenicochroite, also known as melanochroite, is a lead chromate mineral with formula Pb2OCrO4. It forms striking orange red crystals. It was first discovered in 1839 in Beryozovskoye deposit, Urals, Russia. It is named from the Greek word φοίυικος for "deep red" and χρόα for "color", in allusion to its color.

<span class="mw-page-title-main">Lead(II) chromate</span> Chemical compound

Lead(II) chromate is an inorganic compound with the chemical formula PbCrO4. It has a vivid yellow color and is generally insoluble. Two polymorphs of lead chromate are known, orthorhombic and the more stable monoclinic form. Monoclinic lead chromate is used in paints under the name chrome yellow, and many other names. It occurs also as the mineral crocoite.

<span class="mw-page-title-main">Fornacite</span>

Fornacite is a rare lead, copper chromate arsenate hydroxide mineral with the formula: Pb2Cu(CrO4)(AsO4)(OH). It forms a series with the phosphate mineral vauquelinite. It forms variably green to yellow, translucent to transparent crystals in the monoclinic – prismatic crystal system. It has a Mohs hardness of 2.3 and a specific gravity of 6.27.

<span class="mw-page-title-main">Chrome orange</span> Chemical compound and inorganic pigment

Chrome orange is a mixed oxide with the chemical formula Pb2CrO5. It can be made by treating a lead(II) salt with an alkaline solution of a chromate or by treating chrome yellow (PbCrO4) with strongly basic solution.

<span class="mw-page-title-main">Piemontite</span>

Piemontite is a sorosilicate mineral in the monoclinic crystal system with the chemical formula Ca2(Al,Mn3+,Fe3+)3(SiO4)(Si2O7)O(OH). It is a member of the epidote group.

<span class="mw-page-title-main">Tsumebite</span>

Tsumebite is a rare phosphate mineral named in 1912 after the locality where it was first found, the Tsumeb mine in Namibia, well known to mineral collectors for the wide range of minerals found there. Tsumebite is a compound phosphate and sulfate of lead and copper, with hydroxyl, formula Pb2Cu(PO4)(SO4)(OH). There is a similar mineral called arsentsumebite, where the phosphate group PO4 is replaced by the arsenate group AsO4, giving the formula Pb2Cu(AsO4)(SO4)(OH). Both minerals are members of the brackebuschite group.

<span class="mw-page-title-main">Malayaite</span>

Malayaite is a calcium tin silicate mineral with formula CaSnOSiO4. It is a member of the titanite group.

<span class="mw-page-title-main">Tsumcorite</span>

Tsumcorite is a rare hydrated lead arsenate mineral that was discovered in 1971, and reported by Geier, Kautz and Muller. It was named after the TSUMeb CORporation mine at Tsumeb, in Namibia, in recognition of the Corporation's support for mineralogical investigations of the orebody at its Mineral Research Laboratory.

Georgerobinsonite, named for George Willard Robinson, is a lead chromate mineral with formula Pb4(CrO4)2(OH)2FCl. It exhibits very small, transparent crystals with a bright orange-red color. It was obtained from the Mammoth–St. Anthony Mine in Arizona in the 1940s and identified in 2009.

<span class="mw-page-title-main">Hemihedrite</span>

Hemihedrite is a rare lead zinc chromate silicate mineral with formula Pb10Zn(CrO4)6(SiO4)2(F,OH)2. It forms a series with the copper analogue iranite.

<span class="mw-page-title-main">Carminite</span> Anhydrous arsenate mineral containing hydroxyl

Carminite (PbFe3+2(AsO4)2(OH)2) is an anhydrous arsenate mineral containing hydroxyl. It is a rare secondary mineral that is structurally related to palermoite (Li2SrAl4(PO4)4(OH)4). Sewardite (CaFe3+2(AsO4)2(OH)2) is an analogue of carminite, with calcium in sewardite in place of the lead in carminite. Mawbyite is a dimorph (same formula, different structure) of carminite; mawbyite is monoclinic and carminite is orthorhombic. It has a molar mass of 639.87 g. It was discovered in 1850 and named for the characteristic carmine colour.

References

  1. ↑ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi: 10.1180/mgm.2021.43 . S2CID   235729616.
  2. ↑ "Crocoite (PbCrO4)" (PDF). Rruff.geo.arizona.edu. Retrieved 19 December 2016.
  3. ↑ "Crocoite: Crocoite mineral information and data". Mindat.org. 15 December 2016. Retrieved 19 December 2016.
  4. ↑ "Crocoite Mineral Data". Webmineral.com. Retrieved 19 December 2016.
  5. 1 2 3 Chisholm 1911.
  6. ↑ Lehmann, J.G. (1766). De Nova Minerae Plumbi Specie Crystallina Rubra (in Latin). Retrieved 9 November 2018.
  7. ↑ Francois-Sulpice Beudant (1832). Traite elementaire de Mineralogie. 2. ed. Verdiere. p. 669.
  8. ↑ Moore, Thomas P.; Wilson, Wendell E. "Major Crocoite Discoveries" (PDF). The Mineralogical Record. 43: 651–673.
  9. ↑ "Archived copy" (PDF). www.kremer-pigmente.com. Archived from the original (PDF) on 23 March 2014. Retrieved 13 January 2022.{{cite web}}: CS1 maint: archived copy as title (link)
  10. ↑ For $300,000, you could own a hobby mine in a Tasmanian ghost town, Damian McIntyre, ABC News Online, 26 April 2019
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