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Formula: Ca8(Si2O7)2F4
Sorosilicate (Si2O7 groups),
wöhlerite group
Crystal System: Monoclinic
Specific gravity: 2.97 to 2.99 measured, 2.98 calculated
Hardness: 5 to 6
Streak: White
Colour: Colourless, tan, light brown, pale red.
Common impurities: Mn,Na,K,Cl
Environments
Cuspidine is an uncommon sorosilicate. Associated minerals include
augite,
hornblende, diopside,
grossular, biotite,
phlogopite, monticellite,
wollastonite, calcite,
spinel, magnetite and
perovskite
(HOM, Dana).
Localities
At the Shijiang Shan-Shalonggou mining area, Inner Mongolia, China, the mineral deposits occur predominantly in
veins of hydrothermal origin in skarn. Cuspidine was first
identified on 2013 Shijiangshan specimens. Only a very few pieces with cuspidine were recovered, with crystals
up to about 1 cm, sometimes associated with vesuvianite or
andradite. Cuspidine proved to be abundant on 2017–2018 specimens,
occurring as drusy coatings and masses to about 1 cm, commonly in association with
olshanskyite, roweite and
johnbaumite
(R&M 96.5.400-401).
At the Dupezeh Mountain, Iraq, cuspidine occurs in melilite
skarn
(HOM).
At the type locality, Monte Somma, Somma-Vesuvius Complex, Naples, Campania, Italy, cuspidine has been found
in ejected masses
(Webmin, HOM).
At Novinka, Yakutia, Russia, cuspidine has been found in a
kimberlite pipe
(Dana).
At Franklin, New Jersey, USA, cuspidine occurs in
contact metamorphosed
limestone
(HOM).
It is in apparent chemical equilibrium with glaucochroite, which is
younger, and hardystonite, which is altered in some specimens to
clinohedrite. Cuspidine also occurs, within assemblages of
glaucochroite crystals, as a late-stage mineral, forming druses with
clinohedrite in solution vugs in
willemite
(AM 72.423).
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