Axinite-(Mg)

Formula: Ca₄Mg₂Al₄[B₂Si₈O₃₀](OH)₂
Sorosilicates (Si₂O₇ groups), axinite group
Crystal System: Triclinic
Specific gravity: 3.16 measured, 3.167 calculated
Hardness: 6½
Streak: White
Colour: Pale blue
Solubility: Insoluble in water, hydrochloric, nitric and sulphuric acid
Common impurities: Ti,V,Mn,Zn,K,H₂O
Environments:

Metamorphic environments

Axinite-(Mg) is typically formed during contact metamorphism and boron metasomatism (HOM). It was first found in alluvium, later found in contact-metasomatic skarn, associated with epidote, calcite, tremolite - actinolite, vesuvianite and prehnite (Dana).

Localities

At London Bridge, Googong Dam, Queanbeyan, Murray county, New South Wales, Australia, axinite-(Mg) is associated with epidote, tremolite and calcite (HOM).

At the type locality, the Merelani Hills, Lelatema Mountains, Simanjiro District, Manyara Region, Tanzania, an interesting specimen has been found with a 1-cm cluster and a few smaller crystals of tabular axinite-(Mg) crystals, close to pure end-member composition. Other minerals occurring on the same specimen include fluorapatite, chabazite-Ca, diopside, graphite, gypsum, mesolite, pyrite, siderite, tremolite and zoisite variety tanzanite (R&M 88.2.154-165).

At Luning, Mineral county, Nevada, USA, axinite-(Mg) is associated with prehnite, epidote, actinolite and vesuvianite (HOM).

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