BH250-80
Title
BH250-80
Subject
Serpentinized Peridotite
Description
Major Minerals: serpentine, olivine, orthopyroxene, clinopyroxene
Minor Minerals: magnetite
Serpentinized peridotite forms when peridotite, an ultramafic rock rich in olivine and pyroxene, undergoes serpentinization—a hydrothermal alteration process that occurs when the rock interacts with water. This typically takes place at tectonic settings such as mid-ocean ridges, subduction zones, or within ophiolite complexes. During serpentinization, olivine reacts with water to form serpentine minerals, magnetite, while pyroxene alters to serpentine plus talc or tremolite depending on the specific conditions.
The mineralogy of serpentinized peridotite is dominated by serpentine group minerals, including lizardite (massive), antigorite (bladed), and chrysotile (fibrous), often with relict cores of olivine and pyroxene preserved within the serpentine matrix.
Texturally, serpentine replaces olivine along fractures producing a characteristic mesh texture visible in thin section. Serpentine can also pseudomorphically replace original minerals, preserving their crystal shapes. In thin section, serpentine displays low birefringence with a fibrous or platy habit, whereas relict olivine and pyroxene show higher relief and, in the case of pyroxene, distinct cleavage.
Minor Minerals: magnetite
Serpentinized peridotite forms when peridotite, an ultramafic rock rich in olivine and pyroxene, undergoes serpentinization—a hydrothermal alteration process that occurs when the rock interacts with water. This typically takes place at tectonic settings such as mid-ocean ridges, subduction zones, or within ophiolite complexes. During serpentinization, olivine reacts with water to form serpentine minerals, magnetite, while pyroxene alters to serpentine plus talc or tremolite depending on the specific conditions.
The mineralogy of serpentinized peridotite is dominated by serpentine group minerals, including lizardite (massive), antigorite (bladed), and chrysotile (fibrous), often with relict cores of olivine and pyroxene preserved within the serpentine matrix.
Texturally, serpentine replaces olivine along fractures producing a characteristic mesh texture visible in thin section. Serpentine can also pseudomorphically replace original minerals, preserving their crystal shapes. In thin section, serpentine displays low birefringence with a fibrous or platy habit, whereas relict olivine and pyroxene show higher relief and, in the case of pyroxene, distinct cleavage.
Creator
Bereket Haileab
Source
From the rock collection of Bereket Haileab. Sample 80. Housed at Carleton College in Minnesota.
Contributor
Isaac Larson
Type
Thin section and hand sample
Relation
Collection
Citation
Bereket Haileab, “BH250-80,” BH250 Mineralogy Teaching Collection, accessed April 25, 2026, https://bereket-haileab.geology.sites.carleton.edu/items/show/90.