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| Sugar Loaf Mountain |
My seven-year old granddaughter
and I visited Sugar Loaf Mountain in Rio
de Janeiro. The
mountain does in fact resemble a sugarloaf, I suppose, but she had no clue and
neither did I, really. Nevertheless, it was a very large igneous plug which I
explained was an intrusive. By its light
color and rather coarse texture I knew it should be called “granite”. The color was due to its silica content,
light colored igneous rocks are called felsic rocks due to the quartz content,
and it was coarse grained because it had cooled slowly underground. It now is exposed; the material into which it
had been intruded has been eroded away.
If it had cooled on the surface, I told her it would be fine grained and
would be called rhyolite. She’s a pretty
sharp kid (she’s my granddaughter) and understood everything perfectly.
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