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Formula: Sr2Al(AsO4)2(OH)
Valence: Sr2+2Al(As5+O4)2(OH)
Arsenate,
brackebuschite supergroup,
strontium-bearing mineral
Crystal System: Monoclinic
Specific gravity: 4.378 calculated
Hardness: 6 to 6½
Streak: Reddish brown
Colour: Bright orange to salmon to brown
Luminescence: Does not fluoresce under LW or SW UV
Solubility: Unreactive and insoluble in 2M and 10% hydrochloric acid and 65% nitric acid
Common impurities:
Environments
Metamorphic environments
Hydrothermal environments
Localities
At the type locality, the Valletta Mine, Vallone della Valletta, Canosio, Cuneo Province, Piedmont, Italy, grandaite has
been discovered on the mine dump. Its origin is related to the reaction between the ore minerals and hydrothermal solutions. It
occurs in thin masses of bright orange to salmon to brown coloured crystals, or infrequently as fan-like aggregates of small
(<1 mm) crystals, with reddish-brown streak and waxy to vitreous lustre. Grandaite is associated with
aegirine, baryte,
braunite, hematite,
tilasite, quartz and unidentified
manganese oxides and silicates
(MM 78.3.757-774).
The deposit is a small Fe-Mn-As deposit in metamorphosed quartzites, high
pressure, low temperature blueschist facies
(HOM).
Grandaite from the Valetta Mine - Image
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