Alluaudite

Formula:  (Na, Ca)Mn2+(Fe3+, Mn2+, Fe2+, Mg)2(PO4)3

Origin of name:  For Francois Alluaud, French mining engineer, Limoges, France, who discovered the species

 

Crystal system:  Monoclinic

Crystal class: 2/m

Twinning: polysynthetic with {-101} as composition plane, seen in thin section

Unit cell: a = 12.004 Å, b = 12.533 Å, c = 6.404 Å, b = 114°22'

 

Colour:  Dull greenish black, green, dirty yellow, brownish yellow to brownish black

Diaphaneity: Sub-translucent to opaque

Luster:

Habit:  Massive, compact granular, radiating fibrous, and globular aggregates

Hardness:  5 to 5.5

Specific gravity: 3.45

Cleavage:  3; {010}, {110} and {1-10} good

Tenacity:

Streak:  Dirty yellow to brownish

 

Synonyms/varieties:

 

Comments:  Series with ferro-alluaudite. Member of the alluaudite group. Very common mineral in granite pegmatites, formed by sodium metasomatism of triphylite-lithiophilite, heterosite-purpurite, or ferrisicklerite; in phosphatic nodules in shales.

 

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