Picrodolerite
“Olivine-enriched dolerite sill rock”
Picrodolerite is an olivine-rich variety of dolerite (diabase) found in the lower portions of thick sills, where dense olivine crystals accumulated by gravitational settling during cooling. It records the process of crystal fractionation playing out within a single sheet of intruded magma.
olivine (abundant), plagioclase, augite, magnetite, ilmenite, minor orthopyroxene
Palisades Sill (New Jersey, USA — olivine-rich layer), Whin Sill (England), Karoo sills (South Africa), Tasmanian dolerite
6-6.5
The 'olivine layer' near the base of the Palisades Sill in New Jersey is a classic field trip destination for geology students — it's one of the clearest examples of gravitational crystal settling in a single intrusion.
Test Your Knowledge
Why is olivine concentrated in the lower portions of thick dolerite sills like the Palisades?
Related Specimens
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