The Grid: A serpentine pseudomorph after carbonate

Cross-polarized light photomicrograph of a thin section of a carbonated ultramafic rock from the Feragen Ultramafic Body (Norway), with grey serpentine surrounded by fine-grained carbonate.
The sample records a long and varied history of fluid-rock interaction: A peridotite reacted with water to serpentinite, which was then brecciated and cemented by calcium carbonate, possibly as part of the stockwork system beneath a hydrothermal field. Later, the calcium carbonate was dolomitised. Finally, dolomite crystals were replaced by serpentine pseudomorphs. A strong coupling of dolomite dissolution and serpentine precipitation allowed for the preservation of the carbonate twin planes.
Image width: 1.5 cm