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clintonite
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Basalt sample returned by Apollo 15, from near a long sinous lunar valley called Hadley Rille. Measured at 3.3 years old.
(Bed) Rocks and (Flint) Stones
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Also called:
Seybertite
Related Topics:
brittle mica
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clintonite

mineral
Also known as: seybertite
Written and fact-checked by
Britannica Editors
Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree....
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History

clintonite, mica mineral, a basic aluminosilicate of calcium, magnesium, and iron. It occurs in chlorite schist (with talc) and in altered limestones. Clintonite is the primary member of a group of micas (also including margarite) in which calcium substitutes for potassium and the silicon content increases. The members of the clintonite group, also called the brittle micas, are harder and more brittle than the common micas. For chemical formula and detailed physical properties, see mica (table).