THE MINERAL SUSSEXITE

• Chemistry: MnBO₂(OH), Manganese Borate Hydroxide.
• Class: Carbonates
• Subclass: Borates
• Uses: a very minor ore of manganese and as mineral specimens.
• Specimens

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Sussexite is a metamorphic borate mineral. It was first described from the famous mines of Franklin, New Jersey, USA. The mines are located in Sussex County, from where sussexite gets its name. The site of first discovery is called the type locality. Other borates that call this locality their type locality include cahnite and roweite. Other borates found at Franklin, but described somewhere else, include canavesite, fluoborite and mcallisterite.

Sussexite forms a series with the mineral szaibelyite, MgBO₂(OH). A series occurs when two or more elements can substitute for each other without much distortion to the crystal structure. Szaibelyite is rich in magnesium while sussexite is enriched in manganese. Sussexite usually contains some magnesium as well as up to 3% zinc. Sussexite forms fibrous veins and masses.

PHYSICAL CHARACTERISTICS:

• Color is white, pink, yellowish white or straw yellow.
• Luster is silky, pearly to earthy.
• Transparency: Specimens are translucent.
• Crystal System is orthorhombic.
• Crystal Habits include fibrous veins and masses.
• Cleavage is perfect.
• Fracture is uneven.
• Hardness is 3 - 3.5.
• Specific Gravity is approximately 3.1 - 3.3 (slightly above average)
• Streak is white.
• Other Characteristics Non-fluorescent, unlike so many other Franklin minerals.
• Associated Minerals include franklinite, calcite, pyrochroite and hematite.
• Notable Occurrence include the type locality of Franklin, Sussex County, New Jersey and Chicagon Mine, Iron County, Michigan, USA and Gonzen Mine, Switzerland.
• Best Field Indicators are crystal habit, locality, luster, color, non-fluorescence and density.