Moody rock star

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7 Responses to “Moody rock star”

  1. The granite in the James River around Richmond is good stuff and has been featured in many geology textbooks.

  2. What’s so special about it?

  3. Sometimes it is noted as an example of the power of erosion, which is well illustrated in your photo. Other times it is included because it is one of the best exposures of a formation called “Petersburg Granite.”

    http://web.wm.edu/geology/virginia/provinces/piedmont/petersburg_granite.html?svr=www

  4. “Biotite-rich schist” — cool.

    Is this moody rock bedrock that’s been eroded down? Does it underlay the whole region?

    Where’s Bosco?

  5. “Don’t touch my biotite!”

  6. Most folks don’t have the Apatite for this, but since you aksed:

    “Light- to dark-gray to pink, fine- to coarse-grained, equigranular to porphyritic, foliated to nonfoliated, ranges from granite to granodiorite in composition; multiple intrusive phases are present. The granite contains xenoliths of biotite gneiss and amphibolite. Mineralogy: quartz + sodic plagioclase + potassium feldspar + biotite +/- hornblende; accessory minerals include ilmenite, magnetite, pyrite, zircon, apatite, titanite, muscovite, and fluorite. Current mapping restricts the Petersburg Granite to a contiguous unit that crops out in the Cities of Richmond and Petersburg; this roughly corresponds to one of four discrete plutons mapped as Petersburg Granite on the 1963 Geologic Map of Virginia. Samples from within this pluton were dated at 330 +/- 8 Ma.”

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