Sulphates - Sulphates, which are insoluble in water and are related chemically to the saline minerals, include a barium compound called barite; celestite, an ore of strontium; and alunite, a basic aluminum and potassium sulphate. Gypsum, a hydrous calcium sulphate, is the source of plaster of Paris.
Transparent crystals of gypsum, known as selenite, split in thin cracks. When calcium sulphate is found uncombined with water, it is called anhydrite. Polyhalite, a hydrous sulphate of potassium, calcium, and magnesium, is found in the Stassfurt deposits in eastern Germany. Sodium sulphate, sold commercially as Glauber's salt, exists in the hydrated form as the natural mineral mirabilite. Epsom salts, hydrous magnesium sulphate, occurs as the mineral epsomite. For commercial purposes, however, Epsom salts is manufactured from other magnesium minerals.
Sulphates: Mineral Types
Included in this class are various subclasses: the Sulfites, theChromates, the Molybdenates, the Selenates and Selenites, theTellurates and Tellurites and the Tungstates.
[http://mineral.galleries.com/]
Sulphates: Anglesite
Anglesite is a rare lead mineral and can be a beautiful specimen. The typically high luster associated with lead minerals, makes them sparkle like gemstones and Anglesite is no exception to the rule. Anglesite's yellow color seen in many specimens is attractive and adds to the specimen's appeal. Anglesite has the same structure as barite (BaSO4) and forms very similar crystals. However, Anglesite has a very high density and even though Barite is a rather heavy mineral, Anglesite is nearly 50% more dense. This important lead ore was first found at Porys Mine on the island of Anglesey, Wales after which it is named. Like most lead minerals, it has a high specific gravity. It is a secondary mineral, formed most often by the oxidation of a primary deposit of galena. It may occur as granular aggregates surrounding a core of galena, with concentric layers of anglesite identifiable by slight colour
changes.
[http://webmineral.com/]
Sulphates: Anhydrite
Anhydrite is a relatively common sedimentary mineral that forms massive rock layers. Anhydrite does not form directly, but is the result of the dewatering of the rock forming mineral Gypsum (CaSO4-2H2O). This loss of water produces a reduction in volume of the rock layer and can cause the formation of caverns as the rock shrinks. Good mineral specimens of Anhydrite were extremely rare dispite its common occurrance. However, fine specimens of Anhydrite have been found in Mexico and Peru that show good crystal habit, a nice blue color and even a play of light internally in the crystal. Naturally occurring anhydrous calcium sulphate. It is used for the manufacture of plaster of Paris and builder's plaster.commercially.
[http://webmineral.com/]
Sulphates: Barite
Barite is a common mineral and makes very attractive specimens. It often is an accessory mineral to other minerals and can make a nice backdrop to brightly colored crystals. At times bladed or tabular crystals of Barite form a concentric pattern of increasingly larger crystals outward. This has the appearance of a flower and when colored red by iron stains, these formations are called "Desert Roses". Because Barite is so common, it can be confused for other minerals. Celestite (SrSO4) has the same structure as barite and forms very similar crystals. The two are indistinguishable by ordinary methods, but a flame test can distinguish them. By scrapping the dust of the crystals into a gas flame the color of the flame will confirm the identity of the crystal. If the flame is a pale green it is barite, but if the flame is red it is celestite. The flame test works because the elements barium (Ba)
and strontium (Sr) react in the flame and produce those colors. Barite is also known as barytes, baryte, and heavy spar, because of its high density. In fact, the term baryte comes from the Greek word baros which means 'heavy'. Baryte is used in the manufacture of paint and paper, and is the greatest single source of the metallic element barium.
[http://webmineral.com/]
Sulphates: Celestite
Celestite is a favorite among mineral collectors. Its sky blue (or celestial) color is very pretty, and is unique in the mineral kingdom. Celestite also forms with other colorful minerals, making very nice combinations. Blue Celestite with bright yellow sulfur is one of the most famous colorful combinations of minerals. Celestite has the same structure as Barite (BaSO4), and forms very similar crystals. The two may seem identical by ordinary methods, but a flame test can distinguish them. By scraping the dust of the crystals into a gas flame, the color of the flame will confirm the identity of the crystal. If the flame is a pale green, it is barite, but if the flame is red, it is celestite. The flame test works because the elements barium (Ba) and strontium (Sr) react with the flame and produce those colors. Normally barite is not blue, but many specimens of blue barite are often
misidentified as celestite. The nice crystals, good luster and attractive blue color make fine specimens of celestite an outstanding mineral for someone's cabinet or display case. Mineral consisting of strontium sulphate, occurring as white or light blue crystals. It is the principal source of strontium.
[http://webmineral.com/]
Sulphates: Crocoite
Crocoite is a rather unusual lead mineral and can be a beautiful and colorful specimen. Crocoite provides a nice color to the mineral kingdom and is well known for its distinctive orange-red color. Its main source of quality specimens comes from the Dundas District of Tasmania, Australia. The crystals there are usually long thin prisms. However, large crystals from this locality have been scarce in the past thirty years. Most specimens do not have any crystals over 5 cm long. Crocoite's high density and luster are the result of its lead content. Some crocoite aggregates are composed of bars and splinters, of differing sizes, going in a dozen different directions and produces a certain character to these specimens that is distinctive of crocoite. Crocoite is also one of the very few chromate minerals. Beautiful specimens that show off crocoite's unique color, high luster and unusual character
are a prized addition to anyones collection. Crocoite \Cro"co*ite\ (kr?"k?-?t), n. [Gr. ???? saffron.] (Min.) Lead chromate occuring in crystals of a bright hyacinth red color; -- called also red lead ore.
[http://webmineral.com/]
Sulphates: Gypsum
Gypsum is one of the more common minerals in sedimentary environments. It is a major rock forming mineral that produces massive beds, usually from precipitation out of highly saline waters. Since it forms easily from saline water, gypsum can have many inclusions of other minerals and even trapped bubbles of air and water. Common mineral composed of hydrous calcium sulphate. A fine grain gypsum, called alabaster is used for ornamental work. Burned gypsum is known as plaster of Paris, because for a long time it was obtained from gypsum quarries of the Montmartre district of Paris.
[http://webmineral.com/]
Sulphates: Linarite
Linarite is colored a bright azure blue color. This beautiful and somewhat rare mineral is usually found as crusts of small crystals. Even with the small crystals, the color is always intense. Azurite is a mineral that can be easily confused with linarite. Linarite does not react at all to dilute hydrochloric acid. Linarite is formed from the oxidation of lead and copper minerals such as galena and chalcopyrite. The color is impressive for the tiny sparkling crystals. One look at the mineral will convince most collectors that they need an example of linarite in their collections.
[http://webmineral.com/]
Sulphates: Class 6a Minerals
Class 6a Sulphates Class 6b Chromates, Tungstates, Molybdates, Wolframates.
[http://bashrox.net/]
