BH250-87b
Title
BH250-87b
Subject
Komatiite
Description
Major Minerals: olivine (forsteritic composition)
Minor Minerals: serpentine, iron oxides (magnetite)
Textures: spinifex texture, spinifex olivine, sheaf-like olivine aggregates, acicular olivine phenocrysts, olivine pseudomorphs
Alteration: extensive serpentinization of olivine and oxidation to magnetite
BH250-87b is a komatiite specimen from Australia, likely derived from one of the classic Archean greenstone belts of Western Australia, where some of the world’s best-preserved komatiitic sequences occur. Australian komatiites are globally significant because they preserve exceptionally well-developed spinifex textures and are closely associated with economically important nickel sulfide deposits. This sample was collected in Australia and generously donated to the BH250 Collection by John Goodge, Class of 1980.
This specimen expands the geographic scope of the BH250 komatiite suite and allows direct comparison between Canadian and Australian Archean ultramafic volcanic systems. Although both formed from extremely hot magnesium-rich magmas, differences in metamorphic history, deformation, weathering, and alteration can produce noticeable differences in hand sample appearance and thin-section textures.
BH250-87b displays classic bladed to acicular olivine spinifex textures with strong alteration to serpentine and iron oxides. The specimen demonstrates how original olivine crystal morphology can remain remarkably preserved even after extensive metamorphism and hydrothermal replacement. In some areas, radiating sheaf-like aggregates of olivine pseudomorphs create dramatic fan-shaped patterns characteristic of spinifex-textured komatiites.
The Australian specimen is particularly valuable for teaching because it highlights the global distribution of Archean komatiitic volcanism and reinforces the interpretation that hotter mantle conditions were widespread during the Archean Eon. When examined alongside the Munro Township samples, students can compare mineralogy, crystal habit, alteration textures, and preservation styles between different Archean terranes.
Comparative Importance of the Komatiite Suite
Together, BH250-87, BH250-161, and BH250-87b form one of the strongest teaching groups within the BH250 Collection for illustrating:
• Archean mantle temperatures and early Earth volcanism
• Ultramafic lava compositions and high-Mg magmas
• Formation of spinifex textures through rapid crystal growth
• Olivine crystallization and skeletal crystal morphology
• Serpentinization and hydrothermal alteration of ultramafic rocks
• Greenstone belt geology and Archean tectonic environments
• Economic associations with nickel sulfide mineralization
• Variations in preservation between different Archean terranes
These specimens collectively provide students with a rare opportunity to study true komatiites from two classic Archean localities and to directly observe textures that record some of the hottest volcanic eruptions in Earth history.
Minor Minerals: serpentine, iron oxides (magnetite)
Textures: spinifex texture, spinifex olivine, sheaf-like olivine aggregates, acicular olivine phenocrysts, olivine pseudomorphs
Alteration: extensive serpentinization of olivine and oxidation to magnetite
BH250-87b is a komatiite specimen from Australia, likely derived from one of the classic Archean greenstone belts of Western Australia, where some of the world’s best-preserved komatiitic sequences occur. Australian komatiites are globally significant because they preserve exceptionally well-developed spinifex textures and are closely associated with economically important nickel sulfide deposits. This sample was collected in Australia and generously donated to the BH250 Collection by John Goodge, Class of 1980.
This specimen expands the geographic scope of the BH250 komatiite suite and allows direct comparison between Canadian and Australian Archean ultramafic volcanic systems. Although both formed from extremely hot magnesium-rich magmas, differences in metamorphic history, deformation, weathering, and alteration can produce noticeable differences in hand sample appearance and thin-section textures.
BH250-87b displays classic bladed to acicular olivine spinifex textures with strong alteration to serpentine and iron oxides. The specimen demonstrates how original olivine crystal morphology can remain remarkably preserved even after extensive metamorphism and hydrothermal replacement. In some areas, radiating sheaf-like aggregates of olivine pseudomorphs create dramatic fan-shaped patterns characteristic of spinifex-textured komatiites.
The Australian specimen is particularly valuable for teaching because it highlights the global distribution of Archean komatiitic volcanism and reinforces the interpretation that hotter mantle conditions were widespread during the Archean Eon. When examined alongside the Munro Township samples, students can compare mineralogy, crystal habit, alteration textures, and preservation styles between different Archean terranes.
Comparative Importance of the Komatiite Suite
Together, BH250-87, BH250-161, and BH250-87b form one of the strongest teaching groups within the BH250 Collection for illustrating:
• Archean mantle temperatures and early Earth volcanism
• Ultramafic lava compositions and high-Mg magmas
• Formation of spinifex textures through rapid crystal growth
• Olivine crystallization and skeletal crystal morphology
• Serpentinization and hydrothermal alteration of ultramafic rocks
• Greenstone belt geology and Archean tectonic environments
• Economic associations with nickel sulfide mineralization
• Variations in preservation between different Archean terranes
These specimens collectively provide students with a rare opportunity to study true komatiites from two classic Archean localities and to directly observe textures that record some of the hottest volcanic eruptions in Earth history.
Coverage
Australia, collected by John Goodge '80
Creator
Bereket Haileab
John Goodge '80
John Goodge '80
Source
From the rock collection of Bereket Haileab. Sample BH250-87b. Housed at Carleton College in Minnesota.
Contributor
Bereket Haileab
John Goodge '80
John Goodge '80
Type
Thin section and hand sample
Relation
Collection
Citation
Bereket Haileab
John Goodge '80, “BH250-87b,” BH250 Mineralogy Teaching Collection, accessed October 22, 2026, https://bereket-haileab.geology.sites.carleton.edu/items/show/100.