Blackwall Rock
“Dark reaction rind at ultramafic contacts”
Blackwall rock is a dark, chlorite- and amphibole-rich metamorphic rock that forms as a reaction zone between ultramafic rocks (like serpentinite) and adjacent country rock. Chemical exchange between these incompatible rock types produces distinctive concentric mineral zones — a geological boundary layer.
chlorite, actinolite, talc, biotite, magnetite, vermiculite, chromite
Appalachian serpentinite bodies (USA), Franciscan Complex (California), Alpine ophiolites, Barberton Greenstone Belt (South Africa)
3-5
Blackwall zones are so chemically distinct from surrounding rocks that they host unique plant communities — the nutrient-poor, magnesium-rich soil supports rare, specialized plant species found nowhere else.
Test Your Knowledge
What ecological phenomenon occurs on soils derived from blackwall rocks and serpentinites?
Related Specimens
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