Spinelite

Spinelite is a mineral species within the spinel group, named for its spinel-like crystal structure. It is described by the characteristic AB2O4 formula of spinels, with the A-site typically hosting divalent cations and the B-site trivalent cations. An idealized composition is commonly represented as (Mg,Fe2+)Al2O4, with possible substitutions of Mn2+ or Zn2+ on the A-site and Cr3+ or Fe3+ on the B-site.

Crystallography and physical properties: Spinelite crystallizes in the cubic system and often forms octahedral or spinel-like aggregates. It is isotropic in optical behavior, reflecting its cubic symmetry. The mineral is usually opaque with a vitreous luster, and its color ranges from olive gray to black. The streak is white to light gray. Mohs hardness is typically around 8, and the specific gravity falls in the range of about 3.5 to 4.0.

Occurrence and associations: Spinelite has been reported from ultramafic and metamorphic rock settings where spinel-group minerals crystallize. It commonly occurs with other spinel minerals, chromite, magnetite, and peridot in rock matrices, often as disseminated grains or small aggregates.

Etymology and nomenclature: The name spinelite derives from the resemblance to spinel-type structures and the conventional mineral-suffix -lite, used for minerals.

See also: Spinel, Hercynite, Chromite.