Formula: Mg₃(SiO₄)F₂  the most simple member of the humite polysomatic series

Species:

Colour: Orange-yellow, yellow, orange to brown.

Lustre: Sub-Vitreous, Resinous, Waxy

Hardness: 6 – 6½

Specific Gravity: 3.177

Crystal System: Orthorhombic

Member of: Humite Subgroup > Humite Group

Name: Named in 1926 by Per Geijer after the type locality: The Östanmoss Mine, Norberg, Västmanland, Sweden.

Type Locality: Östanmossa mine, Röberg ore field, Norberg, Västmanland County, Sweden

Isostructural with: Alleghanyite, Chegemite, Chondrodite, Edgrewite, Hydroxylchondrodite, Hydroxylclinohumite, Jerrygibbsite, Kumtyubeite, Leucophoenicite, Manganhumite, Reinhardbraunsite, Ribbeite, Sonolite

Norbergite is a mineral in the humite group. It forms a polysomatic series with chondrodite, humite and clinohumite and it is often found with one or more of these minerals.It is difficult to distinguish minerals in the humite group, as they largely occur in the same environments and localities. Their physical and optical appearances are also similar, as is the occurrence as rounded crystals or anhedral grains. Norbergite is F-dominant, and an hypothetical (OH)-dominant end member may not be stable in the common range of temperatures and pressures in the earth’s crust. Norbergite is almost always found in metamorphic and metamorphosed limestone and dolomites and in the contact (calc-silicate rocks/skarns) between these and other rocks. It is often associated with different ores and other Mg-rich silicates such as phlogopite, tremolite and other Mg-rich minerals such as spinel and magnesite. Fluoborite is also an associate of norbergite at some localities. Norbergite normally occurs as isolated rounded grains, rarely as crude crystals. Well-formed crystals are very rare. The best display specimens come from the Limecrest Quarry, New Jersey – USA.