BH250-9
Title
BH250-9
Subject
Ortho-pyroxenite
Description
Major Minerals: orthopyroxene,
Minor Minerals: clinopyroxene, olivine, oxides
Texture: exsolution lamellae, solid solution between opx and cpx
Physical property: 90 degrees cleavage, pyroxene cleavage
Petrology:
Pyroxenite is an ultramafic, igneous rock composed predominantly of pyroxene minerals, specifically orthopyroxene (opx) and clinopyroxene (cpx), often in nearly equal or varying proportions. In the Webster, North Carolina region, pyroxenites are typically associated with mafic-ultramafic intrusions. These rocks are believed to represent crystallized cumulates from high-temperature mafic magmas or solid residues from partial melting processes in the mantle. BH250-9 is an ortho-pyroxenite with enstatite being the dominant mineral and few olivine, oxides and the exsolved clino-pyrorxene as the makeup of the mineralogy of the rock.
Texture:
In the pyroxene of BH250-9, exsolution lamellae are common, especially in orthopyroxene, where thin blades of clinopyroxene exsolve due to cooling from high temperature solid solutions. The presence of solid solution between orthopyroxene and clinopyroxene indicates high-temperature equilibrium before exsolution, suggesting that the rock crystallized or equilibrated at elevated pressures and temperatures.
Physical and Optical Properties:
Cleavage at ~90° is characteristic of pyroxenes (two cleavages intersecting nearly at right angles). The pyroxenes may show parting, exsolution textures, and pleochroism in thin section, aiding in mineral identification. Orthopyroxene is usually brown to green in thin section; clinopyroxene can be colorless to pale green.
Minor Minerals: clinopyroxene, olivine, oxides
Texture: exsolution lamellae, solid solution between opx and cpx
Physical property: 90 degrees cleavage, pyroxene cleavage
Petrology:
Pyroxenite is an ultramafic, igneous rock composed predominantly of pyroxene minerals, specifically orthopyroxene (opx) and clinopyroxene (cpx), often in nearly equal or varying proportions. In the Webster, North Carolina region, pyroxenites are typically associated with mafic-ultramafic intrusions. These rocks are believed to represent crystallized cumulates from high-temperature mafic magmas or solid residues from partial melting processes in the mantle. BH250-9 is an ortho-pyroxenite with enstatite being the dominant mineral and few olivine, oxides and the exsolved clino-pyrorxene as the makeup of the mineralogy of the rock.
Texture:
In the pyroxene of BH250-9, exsolution lamellae are common, especially in orthopyroxene, where thin blades of clinopyroxene exsolve due to cooling from high temperature solid solutions. The presence of solid solution between orthopyroxene and clinopyroxene indicates high-temperature equilibrium before exsolution, suggesting that the rock crystallized or equilibrated at elevated pressures and temperatures.
Physical and Optical Properties:
Cleavage at ~90° is characteristic of pyroxenes (two cleavages intersecting nearly at right angles). The pyroxenes may show parting, exsolution textures, and pleochroism in thin section, aiding in mineral identification. Orthopyroxene is usually brown to green in thin section; clinopyroxene can be colorless to pale green.
Coverage
Location: Webster, North Carolina, USA
Creator
Bereket Haileab
Source
From the rock collection of Bereket Haileab. Sample BH250-9. Housed at Carleton College in Minnesota.
Type
Thin section and handsample
Relation
Collection
Citation
Bereket Haileab, “BH250-9,” BH250 Mineralogy Teaching Collection, accessed April 25, 2026, https://bereket-haileab.geology.sites.carleton.edu/items/show/9.