Extinction Angles

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“Maximum extinction angles in the Pyroxene and Amphibole groups. Solid lines indicate extinction angles from c to c; broken lines from c to a. The extinction angle in an amphibole is generally less than 23 degrees; in a pyroxene it is generally greater. “ -Johannsen, 1908


Albert Johannsen A Key for the Determination of Rock-Forming Minerals in Thin Sections (New York, NY: John Wiley & Sons, 1908)


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2400×2186, 506.1 KiB

Large GIF

1024×932, 89.5 KiB

Medium GIF

640×582, 48.9 KiB

Small GIF

320×291, 17.9 KiB