Formula: Mn²⁺BO₂(OH)

Species:

Colour: White, lilac / lavender, black (perhaps due to alteration or inclusions), also golden-brown; colourless in transmitted light

Lustre: Silky, Dull, Earthy

Hardness: 3

Specific Gravity: 3.30

Crystal System: Orthorhombic

Name: Named in 1868 by George Jarvis Brush after the type localities in Sussex County, New Jersey, USA (location of the Franklin and Sterling Hill orebodies). The name was not explicitly stated to be for “Sussex County” in print, but the understanding was probally known informally and for obvious reasons.

Co-Type Localities: Franklin Mine, Franklin, Franklin Mining District, Sussex County, New Jersey, USA; Hamburg Mine (Hamburg Road Mine), Franklin Mine, Franklin, Franklin Mining District, Sussex County, New Jersey, USA; Trotter Mine (Lehigh Mine; Trotter Shaft; Trotter Dump), Franklin Mine, Franklin, Franklin Mining District, Sussex County, New Jersey – USA

Often fibrous to acicular. At the type localities, often found in fine-grained cherty masses varying in color from pale purple, lilac, lavender, or rose pink or in white to tan fibrous veins. Sussexite-Szaibélyite Series. The manganese analogue of Szaibélyite.