Formula: Mg3(SiO4)F2
Nesosilicate (insular SiO4 groups), humite subgroup,
humite group
Crystal System: Orthorhombic
Specific gravity: 3.177 measured, 3.186 calculated
Hardness: 6 to 6½
Streak: White
Colour: Orange-yellow, yellow, orange to brown
Solubility: Soluble in hydrochloric acid producing a silica gel (Dana)
Common impurities: Ti,Al,Fe,Mn,Zn,Ca,H2O
Environments
Norbergite occurs in contact metamorphic rocks,
marble, magnesium-rich skarn, and at
the contact between calcite-dolomite
marble and granite
(Dana, HOM).
Associated minerals include dolomite, calcite,
fluorapatite, tremolite,
graphite, pyrrhotite,
grossular, wollastonite,
forsterite, diopside,
monticellite, cuspidine,
fluoborite, ludwigite,
fluorite, phlogopite and
brucite
(HOM, Dana, Mindat).
Localities
At the type locality, the Östanmossa mine, Röberg ore field, Norberg, Västmanland County, Sweden, norbergite is associated
with tremolite and a variety of allanite
replacing a dolomitic limestone.
Chondrodite is abundant in other parts of the same mine
(AM 12.266).
At Franklin, New Jersey, USA, norbergite occurs in a coarsely crystalline limestone
from the Nicoll Quarry, In thin sections many of the norbergite grains show irregular cores of
chondrodite and this suggests that the norbergite may have replaced the
chondrodite
(AM 13.349-353).
Amity, Town of Warwick, Orange county, New York, USA, is an area of
granite intrusions into
marble and associated
gneiss. The marble is
mostly composed of white crystalline calcite that often has small flakes
or spheres of graphite and
phlogopite. Norbergite occurs as small yellow masses in
marble, associated with fluoro-edenite and
graphite
(R&M 96.5.438).
In the Grenville marbles near Balmat, St Lawrence county, New York, USA, norbergite, calcite, minor
graphite, pyrite,
fluorapatite and sphalerite are associated
with fluorophlogopite
(AM 67.538-544, 545-557).
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