barredolivine

Barredolivine is a mineral described as a rare variety within the olivine group that displays pronounced barred zoning. It is characterized by alternating, lamellar bands within a single crystal, each band differing in magnesium–iron content and giving a barred appearance under illumination. The mineral follows the general olivine formula (Mg,Fe)2SiO4, with the Mg/Fe ratio varying between bands. Barredolivine crystallizes in the orthorhombic system and shares the framework of olivine minerals.

Occurrence and formation of barredolivine are typically associated with ultramafic rocks where rapid crystallization or diffusion-limited growth promotes zoning patterns. It has been reported in peridotite and related rocks, and may also appear as an exsolution product in high-temperature metamorphic contexts or, in rare cases, in meteorites containing olivine.

Physical and optical properties of barredolivine are consistent with other olivines: color ranges from olive-green to green, with high relief under a microscope. Hardness is about 6.5 to 7 on the Mohs scale. Optical properties include noticeable pleochroism and moderate birefringence, while the barred bands are typically visible in transmitted light under cross-polarized illumination.

Taxonomy and terminology differ among sources. The name barredolivine reflects its characteristic barred zoning. Some authorities treat barredolivine as a textural variety or exsolution feature within olivine rather than a distinct mineral species, pending formal review and acceptance by mineralogical nomenclature authorities.

See also: Olivine, Forsterite, Fayalite, Exsolution.