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Formula: (Mg,Fe,Zn,Ti)4(Al,Fe)10O19(OH)
Oxide, högbomite group
Specific gravity: 3.699 to 3.8 measured
Hardness: 6½
Streak: Grey
Colour: Yellowish, brownish, black
Environments
Magnesiohogbomite-2N 3S occurs in metamorphosed iron ore deposits.
Localities
At lots 10 and 11 of concession 1, Bathurst Township, Lanark County, Ontario, Canada (DeWitts corner), the deposit is
located in the Grenville Geological Province, which consists mostly of
marble, gneiss, and
quartzite.
Syenite-migmatite was
also reported in the area where the vein-dikes are located. Characteristic features of the vein-dikes include the
fact that perfectly formed euhedral crystals of different minerals can often be found floating in
calcite with no points of contact with the walls. Sometimes these crystals
have inclusions of calcite, irregular or rounded in shape. It has been argued
that at least some of the vein-dikes were formed as a result of melting of Grenville
marble.
The two polytypes magnesiohögbomite-6N 12S and
magnesiohögbomite-2N3S are about equally abundant at the
occurrence, and are visually indistinguishable. Magnesiohögbomite is a relatively common mineral at the
locality. It occurs as lustrous dark brown to black crystals to 5 mm, showing flat pinacoid faces and hexagonal
pyramid faces, often striated. Striated hexagonal prism faces are also observed on some crystals. Short-prismatic
crystals with pyramid and prism faces have a barrel shape. Most commonly magnesiohögbomite forms thin tabular
crystals as epitactic overgrowths on spinel. Rarely freestanding crystals,
tabular and short-prismatic, can be found on, or in, spinel and, sometimes,
corundum and calcite.
Magnesiohögbomite has been found both in lot 10 and in lot 11
(R&M 97.6.556-564).
There are two co-type localities, the Dentz Farm, Gravelotte, Murchison Range, Ba-Phalaborwa Local Municipality,
Mopani District Municipality, Limpopo, South Africa, and Mautia Hill, Kongwa, Kongwa District, Dodoma Region, Tanzania.
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