[Rockhounds] photo of an igneous intrusion

[Thomas Yancey]

Nice example of an aplite dike. The fine grained opposite of 
pegmatite (which is characterized by coarse grained to very large 
crystals).

Tom Yancey


>FYI --
>
>   http://silgro.com/photos/090605_BobcatRidgeHike/I_PegmatiteVein.htm
>
>"Now here was an interesting rock -- and I saw similar veins in other
>places.  What happened is that hot magma forced its way into metamorphic
>rock, I would call it a slaty gneiss (but what do I know?)  The pink
>intrusion, probably orthoclase feldspar, must have cooled relatively
>quickly because it's fine-grained.  Note how it "baked" or otherwise
>altered the surrounding stone, darkening it."
>
>This is in the foothills west of Fort Collins, Colorado.
>
>Cheers,
>Alan Silverstein
>--
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