Jeffersonite is a dark green pyroxene mineral, a manganese zinc enriched variety of augite [Ca(Mn, Zn, Fe)Si2O6], sometimes compared to aegirine. It is a mineral consisting of a dark green or greenish black pyroxene. It contains zinc. Jeffersonite is not a recognized mineral name. It is a variety of Augite rich in manganese and zinc, found in the Franklin District, Sussex Co., New Jersey and surrounding areas in the Franklin Marble.
- Formula: Ca(Mn, Zn, Fe)Si2O6
- Specific Gravity: 3.51 – 3.55
- Crystal System: Monoclinic
- Fracture: Uneven to splintery
- Tenacity: Brittle
Properties of Jeffersonite
- Luster: Resinous, Waxy, Sub-Metallic, Dull
- Color: Dark olive green to dark brown
- Streak: Light green
- Hardness: 4½ – 5 on the Mohs scale
- Comment: Softer when leached
- Cleavage: Very Good
- Density: 3.51 – 3.55 g/cm3 (Measured)
It occurs in pegmatites where it can form crystals up to 30 cm (12 in) long and in the contact metamorphic zone between limestone and various intrusive rocks. It is reported from the Sterling Hill Mine, Franklin, New Jersey, in South Australia and Sweden.