Sussexite is a manganese borate mineral MnBO₂(OH). Crystals are monoclinic prismatic and typically fibrous in occurrence. Colour is white, pink, yellowish white with a pearly lustre. It has a Mohs hardness of 3 and a specific gravity of 3.12.^[3]

Sussexite
Sussexite from Mine Hill, New Jersey
General
Category	Nesoborates
Formula (repeating unit)	MnBO2(OH)
IMA symbol	Ssx[1]
Strunz classification	6.BA.15
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	P21/c
Identification
Color	White to buff, lilac/lavender,[2] pale pink, colorless in transmitted light[2]
Crystal habit	As bladed acicular crystals, to 7 mm; cross-vein or radial fibrous, in felted or matted aggregates, nodular.[2]
Luster	Silky, dull(earthy)[2]
Specific gravity	3.30

It is named after the Franklin Mining District in Sussex County, New Jersey, US where it was first discovered in 1868.

Sussexite also occurs in France, Italy, Namibia, North Korea, South Africa, Switzerland, and the US states of Michigan, New Jersey, Utah and Virginia.