THE ALUNITE GROUP OF MINERALS

The Alunite Group is composed of minerals with a similar trigonal structure and related chemistry. It is named for its most common member, alunite. The general formula for this group is AB3(SO4)2(OH)6. The A ions can be either potassium, sodium, calcium, lead, silver or even ammonia (NH4). If A is calcium, silver or lead (at positive two charge) then they will replace two sodiums, potassiums or ammonia (each at positive one charge) and all other elements will be doubled in the formula. The B ions are at a positive three charge and can be aluminum, copper or iron. The structures are of these minerals are rather similar and therefore they form similar crystal habits.

The following are some of the members of the Alunite Group of minerals:

Alunite (Potassium Aluminum Sulfate Hydroxide)
Ammonioalunite (Ammonia Aluminum Sulfate Hydroxide)
Argentojarosite (Silver Iron Sulfate Hydroxide)
Jarosite (Potassium Iron Sulfate Hydroxide)
Minamite (Sodium Potassium Calcium Aluminum Sulfate Hydroxide)
Natrojarosite (Sodium Iron Sulfate Hydroxide)
Plumbojarosite (Lead Iron Sulfate Hydroxide)

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