BH250-245
Title
BH250-245
Subject
Kimberlite
Description
Major Mineral: clinopyroxene, calcite
Kimberlite is a rare, volatile-rich ultramafic igneous rock best known as the primary host of diamonds, though many occurrences are barren. The specimen described here, from the Upper Peninsula of Michigan, is characterized by clinopyroxene and calcite, reflecting strong alteration and the influence of late-stage carbonate-rich fluids. Kimberlites originate deep in the mantle, often at depths greater than 150 km—and are rapidly emplaced to the surface in explosive eruptions that form pipe-like bodies.
This particular sample is highly weathered, which significantly affects both its appearance and mineralogy. In hand sample, it likely appears soft, friable, and earthy, with colors ranging from yellowish to brown due to alteration. Primary minerals such as olivine are commonly completely altered to serpentine and carbonate, explaining the abundance of calcite. The intense weathering also enhances the rock’s crumbly texture and can obscure original igneous features, although relict clinopyroxene may still be preserved.
Kimberlite commonly contains fragments of mantle and crustal rocks (xenoliths), and even when heavily altered, it remains important for understanding deep Earth processes. The dominance of carbonate in this sample points to CO₂-rich magmatic fluids, a hallmark of kimberlite systems. Although Michigan is not a classic locality for diamond-bearing kimberlite, occurrences in the Upper Peninsula are associated with ancient cratonic lithosphere and provide valuable insight into mantle-derived magmatism, volatile transport, and rapid ascent of magma.
Kimberlite is a rare, volatile-rich ultramafic igneous rock best known as the primary host of diamonds, though many occurrences are barren. The specimen described here, from the Upper Peninsula of Michigan, is characterized by clinopyroxene and calcite, reflecting strong alteration and the influence of late-stage carbonate-rich fluids. Kimberlites originate deep in the mantle, often at depths greater than 150 km—and are rapidly emplaced to the surface in explosive eruptions that form pipe-like bodies.
This particular sample is highly weathered, which significantly affects both its appearance and mineralogy. In hand sample, it likely appears soft, friable, and earthy, with colors ranging from yellowish to brown due to alteration. Primary minerals such as olivine are commonly completely altered to serpentine and carbonate, explaining the abundance of calcite. The intense weathering also enhances the rock’s crumbly texture and can obscure original igneous features, although relict clinopyroxene may still be preserved.
Kimberlite commonly contains fragments of mantle and crustal rocks (xenoliths), and even when heavily altered, it remains important for understanding deep Earth processes. The dominance of carbonate in this sample points to CO₂-rich magmatic fluids, a hallmark of kimberlite systems. Although Michigan is not a classic locality for diamond-bearing kimberlite, occurrences in the Upper Peninsula are associated with ancient cratonic lithosphere and provide valuable insight into mantle-derived magmatism, volatile transport, and rapid ascent of magma.
Coverage
Location: Upper peninsula, Michigan, USA
46° 10' 29'' N , 88° 10' 37'' W
46° 10' 29'' N , 88° 10' 37'' W
Creator
Bereket Haileab
Source
From the rock collection of Bereket Haileab. Sample 245. Housed at Carleton College in Minnesota.
Type
Thin section and hand sample
Relation
Collection
Citation
Bereket Haileab, “BH250-245,” BH250 Mineralogy Teaching Collection, accessed April 24, 2026, https://bereket-haileab.geology.sites.carleton.edu/items/show/325.