Add '1911 Encyclopædia Britannica/Variolites'

1911-Encyclop%C3%A6dia-Britannica%2FVariolites.md

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+<br>Other variolites are glassy or partly crystalline facies of olivine-free dolerites, occurring as thin dikes or intrusions, or at the margins of dolerite masses. In these the felspars are well crystallized as thin rods, with square or forked ends, radiating outwards from a centre. They are commonly oligoclase, and sometimes assume branching or feathery forms. Some authors would call these "sphaero-crystals" rather than spherulites