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Formula: Mg7(SiO4)3(F,OH)2
Nesosilicate (insular SiO4 groups), humite subgroup,
humite group, forms a solid solution with
manganhumite
(Dana).
Crystal System: Orthorhombic
Specific gravity: 3.20 to 3.32 measured, 3.201 calculated
Hardness: 6
Streak: White
Colour: White, yellow, dark orange or brown
Solubility: Soluble in hydrochloric and sulphuric acid with the production of silica gel; gives up fluorine in concentrated
sulphuric acid
(Dana).
Common impurities: Ti,Al,Mn,Ca
Environments
Humite occurs in metamorphosed and metasomatised inpure limestone and
dolostone adjacent to acid and less frequently alkaline plutonic rocks, especially
where metasomatism has introduced iron, boron and fluorine
(DHZ1A, Dana).
It is commonly interleaved with clinohumite
(Webmin).
Associated minerals include grossular,
wollastonite,
forsterite, monticellite,
cuspidine, fluoborite,
ludwigite, spinel,
brucite, calcite,
dolomite, serpentine,
diopside, corundum,
phlogopite and pyrrhotite
(DHZ1A, HOM)
The humite group minerals alter readily to serpentine,
chlorite and calcite
(DHZ1A).
Localities
The type Locality is Monte Somma, Somma-Vesuvius Complex, Naples, Campania, Italy.
At Anzahamarono, Madagascar, humite occurs in marble with
spinel
(Dana).
In the Glomfjord area, northern Norway, humite occurs in chondrodite - humite -
spinel - brucite -
calcite - pyrrhotite assemblages in
marble; the chondrodite and humite are
commonly interleaved and both minerals are partially replaced by brucite
(DHZ1A).
At the South Harris igneous complex, Outer Hebrides, Scotland, UK, humite occurs in
forsterite
and diopside marble xenoliths
within metamorphosed
tonalite, chondrodite and
humite both occur as
small rounded grains along the margins of
partly serpentinised crystals of forsterite
(DHZ1A).
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