Clinochlore

clinochlore

chamosite

phlogopite

chlorite

Images

Formula: Mg5Al(AlSi3O10)(OH)8
Phyllosilicate (sheet silicate), chlorite group, forms a series with chamosite
Specific gravity: 2.6 to 3.02
Hardness: 2 to 2½
Streak: Greenish white to white
Colour: Green, yellowish green, olive green, blackish green, bluish green, white, pink
Environments

Metamorphic environments
Hydrothermal environments

Clinochlore is frequently a product of contact or low-grade regional metamorphism; it is found in fissure veins, soils, sediments, and amygdules in volcanic rocks. Frequently associated minerals include feldspar, quartz, biotite, garnet, calcite group and dolomite group minerals, magnetite, chromite, talc, serpentine, chloritoid, rutile, ilmenite, titanite, common sulphides, zircon and zeolites; rarely it is found with corundum, diaspore, margarite or spinel. It can be a hydrothermal alteration product of a variety of species including garnet, biotite, pyroxene and amphibole (Dana, HOM).

Localities

The Two Mile and Three Mile deposits, Paddy's River, Paddys River District, Australian Capital Territory, Australia, are skarn deposits at the contact between granodiorite and volcanic rocks. Clinochlore is a primary silicate that occurs in large masses in silicate-rich areas of skarn, and as an alteration product in the surrounding dacitic volcanics. Associated minerals include magnetite, epidote and clinozoisite (AJM 22.1.34).

At Blair Duguid, near Allandale, Hunter valley, New South Wales, Australia, in a small outcrop of andesite, clinochlore occurs rarely, associated with earlier crystallised quartz and later heulandite-Ca (AJM 18.2.31).

At the Mount Kelly deposit, Gunpowder District, Queensland, Australia, the deposit has been mined for oxide and supergene copper ores, predominantly malachite, azurite and chrysocolla. The ores overlie primary zone mineralisation consisting of quartz-dolomite-sulphide veins hosted in dolomite-bearing siltstone and graphitic schist.
Clinochlore is relatively abundant as an alteration phase within some of the host siltstone, mostly replacing detrital biotite (AJM 22.1.17).

At Coobina, Pilbara province, Western Australia, chromium-rich clinochlore occurs in seams hosted in ultramafic rocks. Pegmatites intruding the complex exhibit coarse mantles of phlogopite and chlorite at their contact with serpentinite. Some chromium-rich clinochlore occurs in these contact zones, on a chromite matrix and associated with secondary magnesite, antigorite and traces of serpentine. It is suggested that the clinochlore derived from the interaction of granitic fluids and the chromite-rich ultramafic rocks (AJM 16.1.35-37).

At the Alpine-type Fissures and Talc Deposit at Saint-Pierre-de-Broughton Quebec, Canada, clinochlore occurs as aggregates to 3mm across of pseudohexagonal, platy crystals. Associated minerals include rutile, talc and rarely bastnäsite-(Ce) (R&M 85.6.503).

At Yaogangxian, Yizhang county, Chenzhou, Hunan, China, clinochlore has been reported, possibly as an alteration product of chamosite (Minrec 42.6.578).

At Irkutsk, Russia, clinichlore occurs with magnetite (R&M 85.4.321).

At the Witwatersrand goldfield, South Africa, clinochlore is a secondary mineral commonly associated with fine-grained gold. Green to green-blue clinochlore crystals to a few millimetres are found on secondary quartz and calcite, either coating the crystals or as inclusions inside quartz crystals (R&M 96.4.322).

At the Bastnäs Mines, Riddarhyttan, Skinnskatteberg, Västmanland County, Sweden, clinochlore has been found associated with hematite (Minrec 35.3.195).

At Lane's Hill quarry, Stoney Stanton, Blaby, Leicestershire, England, UK, a specimen has been found that contained well-crystallised, dark green microcrystals of chlorite (possibly clinochlore) that occurred with three generations of Fe-bearing dolomite and later calcite (JRS 20.14).

In San Benito county, California, USA, crystals of clinochlore occur with andradite (R&M 85.4.321).

At the Hunting Hill quarry, Rockville, Montgomery county, Maryland, USA, clinochlore is found as veuns in serpentinite, and as crystals in cavities to 1 cm in rodingite (Minrec 36.5.439).

At the Spurr mine, Michigame, Baraga county, Michigan, USA, clinochlore pseudomorphs after almandine have been found (KL p239).

Amity, Town of Warwick, Orange county, New York, USA, is an area of granite intrusions into marble and associated gneiss. The marble is mostly composed of white crystalline calcite that often has small flakes or spheres of graphite and phlogopite. Clinochlore occurs with serpentine as a massive partial alteration of uvite/fluor-uvite crystals to 2 cm (R&M 96.5.435).

At the Pyrites Mica mine, St Lawrence county, New York, USA, clinochlore forms as an alteration product on the surface of some crystals of meionite, and also as an outer rind on large plates of phlogopite (R&M 93.4.339).

In New York City, USA, clinochlore crystals occur associated with quartz and albite in the rock excavated for the 63rd Street subway in Manhattan. Chrome-rich clinochlore microcrystals on serpentine have been recovered at an exposure on Lincoln Avenue in Staten Island (R&M 84.3.228).

At the Tilly Foster Iron Mine, Brewster, Town of Southeast, Putnam county, New York, USA, crystals of clinochlore with calcite and chondrodite are known (R&M 85.4.320).

At the Pyrites mica mine, St Lawrence county, New York, USA, clinochlore occurs as an alteration product forming on the surface of some crystals of meionite, and also as an outer rind to 1 cm or more on large plates of phlogopite. Some crystals of phlogopite are nearly completely replaced by clinochlore (R&M 93.4.339).

The type locality is Brinton's Quarry, Westtown Township, Chester county, Pennsylvania, USA.

At the Belvidere Mountain Quarries, Lowell & Eden, Orleans & Lamoille counties, Vermont, USA, clinochlore is the major constituent of the serpentine - chlorite contact rocks and the blackwall rock. Crystals of clinochlore to about 4 cm occur in chlorite - calcite - magnetite veins and in cavities in rodingite (R&M 90.6.529).

Alteration

tremolite, anorthite and clinochlore to tschermakite and H2O
3☐Ca2MgSi8O22(OH)2 + 8Ca(Al2Si2O8) + 2Mg5Al(AlSi3O10)(OH)8 ⇌ 5☐Ca2(Mg3Al2)(Si6Al2)O22(OH)2 + 4H2O
(AM 76.998)

Common impurities: Fe2+,Cr,Ca

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