Nesosilicate (insular SiO4 groups), humite group
Specific gravity: 3.177
Hardness: 6 to 6½
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
Norbergite occurs in contact metamorphic rocks,
marble, magnesium-rich skarn, and at
the contact between calcite-dolomite
marble and granite
Associated minerals include dolomite, calcite, fluorapatite, tremolite, graphite, pyrrhotite, grossular, wollastonite, forsterite, diopside, monticellite, cuspidine, fluoborite, ludwigite, fluorite, phlogopite and brucite (HOM, Dana, Mindat).
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).
In the Grenville marbles near Balmat, 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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