Formula: Mn2+BO2(OH)
Anhydrous borate containing hydroxyl, forms a series with szaibélyite
Specific gravity: 3.30
Hardness: 3
Streak: White
Colour: White, lilac/lavender, black (perhaps due to alteration or inclusions), also golden-brown; colourless in transmitted light
Solubility: Slowly soluble in acids
Common impurities: Mg

Metamorphic environments
Hydrothermal environments

Sussexite is a hydrothermal mineral typically in veinlets in boron-bearing metamorphosed manganese-iron-zinc deposits (Webmin, HOM), associated with pyrochroite, rhodochrosite, wiserite, hausmannite, sonolite, alabandite, seamanite, tephroite, alleghanyite, willemite, leucophoenicite and hauckite (HOM).


At Iron county, Michigan, USA, sussexite is associated with seamanite, occurring in thin veinlets 1mm to 3mm wide. The veins run through both hematite ore and highly altered, porous cherty gangue. Small cavities within the veins are lined with crystals of seamanite, in many instances implanted directly upon sussexite (AM 19.575).

Sussexite has three co-type localities, the Hamburg mine, the Trotter mine, and the Franklin mine itself, all at Franklin, Franklin Mining District, Sussex county, New Jersey, USA. Here sussexite occurs in hydrothermal veinlets traversing a Precambrian metamorphosed zinc-manganese-iron orebody, associated with willemite, rhodochrosite, pyrochroite and leucophoenicite (Mindat). A specimen has been found at Franklin furnace consisting chiefly of willemite, franklinite and zincite with a coating of fibrous sussexite (AM 9.188).

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