Chlorine Minerals
by John Betterton
Chlorine, Cl, is a well-known non-metallic element that has a crustal abundance of about 130 ppm. World production stands at over 250 million tonnes per year that is produced by most countries. The main suppliers are China, USA, India, Canada, Brazil and Australia. Planetary servers ...
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are almost limitless. Halite is the main mineral from which this element is extracted and has been described is a previous article in this series.
Some of its uses are as chlorine gas from which numerous products are manufactured i.e. PVC plastics, HCl, in water purification and chlorination, solvents, bleaches, pharmaceuticals, flame retardants, pesticides, cleaning products, food processing, agricultural uses, road deicing, textile production and in many inorganic and organic industrial chemicals.
Chlorine is a very frequent constituent of minerals and is therefore represented in most mineral groupings, particularly in the halides, carbonates, borates, sulphates and silicates.
Djerfisherite, K6(Fe,Cu,Ni)25S26Cl, is a cubic mineral that occurs as small rounded grains with a Greenish-yellow to olive green colour. It is submetallic and opaque.
The hardness is about 3.5 and other properties are unknown. X-ray methods and chemistry are recommended for identification. Djerfisherite occurs in hydrothermal veins, skarns, pegmatites, kimberlites and mafic alkalic diatremes. It is also known from meteorites. Kamacite, troilite, schreibersite, clinoenstatite, tridymite, cristobalite, graphite, alabandite, pentlandite, chalcopyrite, magnetite, sphalerite and other rare minerals are associated with this uncommon species. It occurs in some localities in Canada, China, Greenland, Iraq, Italy, Japan, Norway, Romania, Russia, South Africa and USA.
Dadsonite, Pb23Sb25S60Cl, is a triclinic/monoclinic mineral of hydrothermal deposits. It is accompanied by jamesonite, robinsonite, bournonite, boulangerite, zinkenite and chalcostibite. It is found as minute fibrous needles resembling steel wool and can be up to about 2 mm in length. Crystals can be striated. The mineral is lead-grey in colour with a metallic lustre. It possesses a black streak and a hardness of 2.5. The specific gravity is 5.6. Chemistry and x-rays are best for characterisation. A range of widespread locations is known for this rare species.
They can be found in Canada, France, Germany, Greece, Italy, Slovakia, Spain and the USA.
Bismoclite, BiOCl, is cream-white, greyish to yellowish brown mineral with a greasy, silky to pearly lustre. It is opaque and transparent in fine grains with a perfect cleavage. The hardness is low at 2-2.5. Its specific gravity is high at 7.3. X-rays and chemical tests required. Bismoclite occurs near Bi-bearing granite pegmatites, greisens, hydrothermal veins and rarely in alluvial deposits. Bismutite, bismuthinite, jarosite, alunite, cerussite, atacamite, connellite, quartz, clinochore and various uranium minerals can be found with bismoclite. Sites that have produced specimens include those in Australia, Bolivia, Brazil, Canada, France, Germany, Italy, Japan, Namibia, Norway, Russia, South Africa, Tajikistan, UK and the USA.
Sylvite, KCl, crystallises in cubic system with cubic, cubo-octahedral and octahedral crystals, generally to several cm in size.
Columnar, granular, massive to compact varieties are also found. It is colourless to white and greyish, bluish, yellowish and red when included with hematite. Aprefect cleavage is present with an uneven fracture and is brittle and ductile.
The hardness is 2 and the specific gravity is low at 1.9. The mineral is soluble in water with a salty but bitter taste. Its lustre is vitreous and is transparent. This mineral can be distinguished from halite by the taste and flame test. Sylvite occurs abundantly in sedimentary basins, forming thick beds, as a sublimate product of volcanic fumaroles, in nitrate beds, caves, and can be found included in minerals derived from intermediate–grade metamorphism. It is commonly found with halite, kieserite, kainite, carnallite, polyhalite, gypsum and anhydrite. Many nations have furnished good quality samples. Typical occurrences are found in Germany, Austria, Italy, England, Ukraine, Russia, China, USA, Canada, Mexico, Australia, Bolivia and other countries.
Phosgenite, Pb2(CO3)Cl2, is an uncommon but very attractive mineral for collectors. It forms tetragonal crystals that are usually short prismatic and commonly terminated.
Thick tabular crystals are rarer. Granular and massive aggregates also occur. It is transparent to translucent with an adamantine lustre. The colour is variable from pale yellow to yellowish brown, pale brown, smoky violet, colourless, pale rose, grey to pale green. Its streak is white with several distinct to indistinct cleavages. The fracture is conchoidal and is sectile and flexible. Hardness is 2 to 3 and varies with direction. It may fluoresce yellow under LW UV light. Chemical tests, morphology and physical tests are needed for identification.
Phosgenite is typically formed by alteration of galena in the oxidation zone of hydrothermal lead deposits or by the reactions of seawater with other Pb mineral species. Cerussite, anglesite, matlockite, laurionite and quartz are usually associated with it. Wonderful examples have been located in England, Italy, Poland, Russia, Germany, Morocco, Namibia, Australia, USA, The mineral is also know from slag sites around the world.
Hilgardite, Ca2B5O9Cl.H2O, is a borate mineral of marine evaporite deposits. Boracite, anydrite, danburite, dolomite, magnesite, pyrite, hauerite, calcite, quartz, sulphur and gypsum commonly occur with this mineral species. It is monoclinic and triclinic in character with distorted triangular crystals with tabular and hemimorphic features. It is transparent to translucent with a vitreous lustre. The mineral may be colourless and slightly reddish brown in colour.
Its streak is white with perfect to good cleavages. The fracture is conchoidal with a hardness of 5. Its specific gravity is 2.6-2.7.
Chemical and physical tests are needed with the above properties. Countries that have supplied specimens include the USA, Canada, Germany, England, Kazakhstan, Russia and Israel.
Chlorapatite, Ca5(PO4)3Cl, occurs as hexagonal prismatic crystals with a variety of different habits. Granular and massive aggregates are common. It is transparent to translucent with a vitreous lustre. Colours range from green, grey, yellow to pink. It possesses poor cleavages and is brittle. The hardness is around 5 and the specific gravity is 3.1. Hardness, crystal system and chemistry are of help here.
Chlorapatite is quite abundant mineral and is formed in fluorine deficient environments such as calcsilicate marbles, layered mafic intrusions, mineral veins, granite pegmatites and in meteorites. It is accompanied by actinolite, diopside, calcite, plagioclase, titanite, datolite, olivines, orthopyroxenes, phlogopite, chromite and ferroalluadite. Good samples may be obtained from the USA, Canada, South Africa, Morocco, India, Japan, Norway (with large crystals!), Sweden, Slovakia, Romania, Italy, Russia, Germany, Chile etc.
Connellite, Cu19Cl4(SO4)(OH)32.3H2O, is a complex uncommon but widespread secondary mineral of oxidised Cu deposits.
Cuprite, spangolite, atacamite, langite, malachite, azurite and botallackite are found with it. This gorgeous species is translucent and azure –blue in colour with a pale greenish blue streak. It forms hexagonal acicular prismatic crystals that are elongated and striated. The mineral usually develops in tight radiating groups.
Fibrous, felted and crusty habits also occur.
Its hardness is 3 and the lustre is vitreous. The specific gravity is 3.3 to 3.4. The mode of occurrence, habit, chemistry and celebrated locations contribute to its identification. This is a collector’s mineral with high prices for splendid specimens. Locations for connellite include those in England, USA, Germany, France, Italy, Austria and Australia. This mineral is increasingly being recognised from other minor localities worldwide.
Sodalite,Na8(Al6Si6O24)Cl2, is a cubic species that rarely forms typical dodecahedrons along with twined crystals.
Elongated pseudohexagonal prisms also occur. It is usually found as massive aggregates and grains. The mineral is transparent to translucent with a vitreous to greasy lustre. Colour is variable from colourless, white, yellow, pink, green to light or dark blue. The streak is white with a poor cleavage and is brittle in character. Its hardness is 5.5 to 6. It possesses an uneven to conchoidal fracture and may give off the odour of hydrogen sulphide on fracture.
Sodalite has a bright red-orange cathodolumescence and fluorescence under LW and SW UV light, with a yellowish phosphorescence and may be photochromic in magenta shades. The specific gravity is 2.2-2.3. Above physical properties, flame test, typical blue colouration and mineralogical environment aids in identification. This is a characteristic mineral of nepheline syenites, phonolites, related rocks and associated pegmatites and dykes. Also is found in metasomatic calcsilicate rocks and in cavities in ejected volcanic blocks. Sodalite is a widespread mineral and prominent locations exist in Greenland, Norway, Russia, Italy, Germany, Afghanistan, USA, Canada, Brazil, Bolivia, Burma, Namibia etc. Massive material is cut into carvings, decorative objects, cabochons, spheres, boxes and beads.
Faceted gems are normally dark except in small sizes. It is commonly acquired from dealers at the Rock n Gem Shows across the UK.
Zunyite, Al13Si5O20(OH,F)18Cl, can be found in excellent tetrahedral or pseudooctahedral crystals up to about 2 cm in size. They may be modified, and contact and penetration twins also occur. It is transparent or nearly opaque due to inclusions. The colour is greyish, white or flesh-red with a vitreous lustre. It is brittle with a good cleavage. The hardness is 7 and may fluoresce red under UV light. Its specific gravity is 2.8. Physical, chemical and mode of occurrence are useful characteristics.
Zunyite is a rare to common mineral of aluminous shales and hydrothermally altered feldspars in volcanic rocks and limestones. Pyrophyllite, kaolinite, alunite, diaspore, rutle, pyrite, hematite and quartz are to be found with it. Examples of this species are known from the USA (with numerous localities in many states), South Africa, Turkey, Spain, Algeria, Morocco, Slovakia, Hungary, Uzbekistan, Japan, Argentina, Chile and Peru.
In the next issue of this magazine we will survey the minerals of hydrogen.
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