metamorphic
Slate with Fossiliferous Impressions
Metamorphosed Argillaceous Rock (Fossiliferous Slate)
Hardness: 2.5-4; Color: Grey-green to charcoal grey; Luster: Dull/Earthy; Crystal structure: Microcrystalline; Cleavage: Slaty cleavage; Grain: Fine-grained
- Hardness
- 2
- Color
- Grey-green to charcoal grey
- Luster
- Dull/Earthy
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Physical properties
Hardness: 2.5-4; Color: Grey-green to charcoal grey; Luster: Dull/Earthy; Crystal structure: Microcrystalline; Cleavage: Slaty cleavage; Grain: Fine-grained
Formation & geological history
Formed through low-grade regional metamorphism of shale or mudstone. The presence of white, curved markings suggest tiny fossilized shell fragments or worm burrows (bioturbation) that survived the heat and pressure. It originated in marine environments during the Paleozoic era.
Uses & applications
Used for roofing tiles, flooring, blackboards, and billard table tops. This specific piece is a common educational sample for demonstrating fossils in metamorphic rocks.
Geological facts
While metamorphism usually destroys fossils, low-grade slate can preserve them as flattened molds or mineralized outlines. This specimen shows 'fossil ghosts' or shell hash remnants.
Field identification & locations
Identify by its ability to split into thin sheets (fission) and the presence of small, white, curved calcitic or quartz-filled inclusions that contrast against the dark background. Found in folded mountain belts like the Appalachians or North Wales.
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