What is Norbergite?
Norbergite is a yellow to orange humite-group silicate from magnesium-rich metamorphic rocks and skarns.
Mineralogy and crystal structure
Reference formula: Mg3SiO4(F,OH)2. Norbergite is an orthorhombic humite-group mineral with fluorine and hydroxyl substitution. It commonly occurs with chondrodite, clinohumite, brucite and spinel in high-temperature calc-silicate assemblages. Norbergite is classified with silicates and has a orthorhombic crystal system. Typical hardness is 6–6.5 on the Mohs scale and specific gravity is approximately 3.1–3.3.
Colour, lustre and habit
Typical colours include yellow, orange, brown, white. The usual prismatic, granular, massive habit and vitreous, pearly lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Norbergite forms in or is associated with marbles, skarns, contact-metamorphic rocks and magnesium-rich ore environments. Important documented localities include Sweden, the United States, Canada, Italy, Pakistan and Madagascar.
Warm colour in a magnesium skarn
Norbergite has the quiet warmth of a honey-yellow crystal but the geological depth of a high-temperature skarn. Its place in the humite group makes it especially useful in comparative collections.
Collecting and care
Protect crystal faces from impact and acids; retain the metamorphic association for identification.
