Jeffersonite is a dark green pyroxene mineral, a manganese zinc enriched variety of augite, chemical formula , sometimes compared to aegirine. Jeffersonite is not a recognized mineral name. It occurs in pegmatites where it can form crystals up to long and in the contact metamorphism, 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.

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MindatAbandoned Mines of New Jersey
Calcium minerals Manganese(II) minerals Iron(II) minerals Zinc minerals Pyroxene group Minerals described in 1822 {{silicate-mineral-stub