The axinite group includes:
axinite-(Fe):
Ca4Fe2+2Al4[B2Si8O30](OH)2
axinite-(Mg):
Ca4Mg2Al4[B2Si8O30](OH)2
axinite-(Mn):
Ca4Mn2+2Al4[B2Si8O30](OH)2
tinzenite:
Ca2Mn2+4Al4[B2Si8O30](OH)2
All of these are triclinic sorosilicates (Si2O7 groups)
Localities
At Heng Fa Chuen, Hong Kong Island, Hong Kong, China, axinite occurs in a
pegmatite at the Chai Wan MTR (Mass Transit Railway) railway depot, just
southeast of the Heng Fa Chuen MTR station, adjacent to the eastern entrance of the MTR railway tunnel. The
pegmatite cavity occurs in medium-grained
granite almost completely devoid of
biotite.
About 20 m away the contact of granite with pyroclastic rocks is exposed.
The pegmatite cavity is about 40 cm wide and contains axinite,
K-feldspar, milky quartz and
muscovite
(Geological Society of Hong Kong newsletter 2.1.9).
At Charcas, Charcas Municipality, San Luis Potosí, Mexico,
the primary minerals are
sphalerite, galena,
chalcopyrite, bornite,
tetrahedrite,
arsenopyrite, pyrite and
silver minerals such as jalpaite,
diaphorite and acanthite. In
the host rock, as metamorphic or alteration minerals, danburite,
datolite, hedenbergite,
epidote, chlorite,
andradite, actinolite
and wollastonite have been reported.
Quartz, calcite and
danburite crystallised during the entire life of the systems, throughout
the intrusive emplacement, metamorphism, and mineralising events. With depth, both
sphalerite and galena decrease
while chalcopyrite increases.
Secondary sulphides formed include
bornite, covellite,
digenite and chalcocite.
Native silver, native gold,
hematite and goethite were
deposited after the sulphides
(Minrec 55.6.727-728).
An axinite group mineral occurs as a skarn-forming mineral in
massive crystal aggregates, associated with other boron minerals such as
danburite and tourmaline in
marble and
wollastonite masses, with sulphides such as
pyrite. More rarely, the axinite mineral occurs in narrow open
fractures as brown, well-formed, elongated tabular crystals with wedge terminations; these can reach 2 cm in
length. The best crystals came from La Aurora mine
(Minrec 55.6.735).
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