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194-Granite and Gabbro $10.00
All Mysteries include a rock, fossil, or mineral sample and Mystery questions with teaching instructions.

-- A piece of granite (for example, from eastern Maine) containing angular pieces (clasts) of
dark-colored gabbro

-- To build on ideas from Mystery #192
-- To reinforce the idea that this igneous rock formed hundreds of meters beneath the ground, where rocks melt to form magma which rises, cools and hardens, then is ultimately exposed by erosion
-- To show that two major igneous rock types, granite and gabbro can occur together even though the magmas have very different origins
-- To introduce the notions that, 1) the broken clasts of gabbro indicate that the gabbro must have been cooled and partly hardened before it was broken into pieces that were incorporated in the soft, molten granite; and 2) that since these breccias are found next to “pillows” known to indicate the intrusion of hot, mafic magma into the cooler granite melt, then the mafic clasts must have been ductile, and rather easily broken, and 3) given that mafic magma intrudes into granite when both are still molten, then we must accept that the two magma types do interact.

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Ruth Deike
Rock Detective Geoscience Education
395 Deer Run Drive
Nellysford , VA 96080

Phone: 434-263-3737



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