Picropharmacolite

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Picropharmacolite
2V angle
40° – 50°
Dispersionr < v strong
Other characteristicsFluorescent blue-white under long wave and short wave ultraviolet light
References[2][3][4][5]

Picropharmacolite, Ca4Mg(AsO3OH)2(AsO4)2·11H2O, is a rare arsenate mineral. It was named in 1819 from the Greek for bitter, in allusion to its magnesium content, and its chemical similarity to pharmacolite. The mineral irhtemite, Ca4Mg(AsO3OH)2(AsO4)2·4H2O, has the same composition as picropharmacolite, except that it has only four water molecules per formula unit, instead of eleven. It may be formed by the dehydration of picropharmacolite.

Structure

hydrogen bonding only. Four independent water molecules are sandwiched between adjacent layers, and build up hydrogen-bonded chains which are also parallel to the c axis. The ratio of four Ca to one Mg remains fairly steady, and no significant Ca/Mg substitution occurs in any cation site. Hence if the formula of picropharmacolite is written as Ca4Mg(H2O)7(AsO3OH)2(AsO4)2.4H2O,[8]
it is a better representation of the structure than the more usual formula Ca4Mg(AsO3OH)2(AsO4)2.11H2O.

Morphology

Picropharmacolite is usually found as small to microscopic pearly white botryoidal aggregates with a radiating foliated structure internally. Less commonly it occurs as silky fibrous aggregates or minute needle-like crystals, that are rectangular prisms elongated along the c axis.

Environment

Formed as an

sulfides in reaction with surrounding calcium-bearing rocks, and as a recent efflorescence in mine workings. Erythrite and pharmacolite are common associated minerals.[3]

Type locality

It was first described for samples from ore dumps of the Richelsdorf Smelter,

References

  1. S2CID 235729616
    .
  2. ^ a b Gaines et al (1997) Dana's New Mineralogy Eighth Edition, Wiley
  3. ^ a b c d http://rruff.geo.arizona.edu/doclib/hom/picropharmacolite.pdf Handbook of Mineralogy
  4. ^ a b "Picropharmacolite".
  5. ^ "Picropharmacolite Mineral Data".
  6. ^ American Mineralogist (1974) 59:807
  7. ^ American Mineralogist (1976) 61:326
  8. ^ American Mineralogist (1981) 66:385

External links