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Post by snowmom on May 31, 2014 14:35:27 GMT -5
and so are my ID skills. There are some I have decided defy description. This trip I got the most colorful and interesting picks yet. Jaspers, quartzite/something in gold that is opaque, odd granites and conglomerates, agatey somethings. What do you think of the thing I am holding in my hand? It seems to be nodules formed separately but all stuck together. Yellow and white, I am not sure if the black is mineral or staining of the matrix, maybe trying to be granite.. in some places there are little blood red veins running around the stones. I got at least 3 which have that in this batch. All were pulled out of water about 9 inches to a foot deep in Lake Huron on the same beach.
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Post by 150FromFundy on May 31, 2014 21:13:04 GMT -5
The first one is probably pegmatite, which is a coarse grained granite. The slower it cools, the larger the crystals grow.
Darryl.
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Post by snowmom on Jun 1, 2014 6:51:59 GMT -5
thanks, looking more closely at it, some of the crystals do seem to be undercut with a bit of black deep in the grooves between them. lake wear does interesting things to rocks here. Looking closely the crystal lumps seem to be calcite, quartz and feldspar, plus those little touches of black stuff between a few of the stones. I love stuff from the lake! Thanks Darryl.
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Post by 150FromFundy on Jun 2, 2014 17:51:26 GMT -5
If there is calcite in that, you will blow my granite/pegmatite theory out of the water. Calcite is soft (2.5 to 3.0 Mohs), should easily scratch with your fingernail, and will fizz if you look closely (hand lens) at a vinegar drop placed on the calcite. Feldspar is hard (6 Mohs) and quartz will scratch glass (7 Mohs).
I'm betting that the variation in colour is either in the feldspar, or some iron staining that may be on the surface only. Wish you had a saw yet? You could cut it and see.
Darryl.
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Post by snowmom on Jun 2, 2014 18:20:48 GMT -5
nope, it isn't calcite then, maybe another form of quartz.. it is hard as the other 2... should have a saw before long. (thanks to Walt), Your pegmatite post sent me off on a google search and I found that a lot of things I had found here( in Alpena or this area) before fit into the pegmatite tag. A few don't, but I guess there are other forms of slow cooling stuff that made big crystals too? I have all sorts of stones that are 3 or 4 sided, different types of stone on each side, or surrounded by basalt or rhyolite matrix, sometimes one type of stone, sometimes a mix of 2 or more kinds of stones. Still confused but the fog clears a bit now and then. thanks for your help!
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Post by Jugglerguy on Jun 2, 2014 19:32:09 GMT -5
I found what I think was pegmatite out near El Cajon bay last year. There was a geocache right by it that my daughter and I went to find. There were lots of bugs and wildflowers on that walk. There were a bunch of endangered dwarf lake irises out there. There is also a large underwater sink hole in the bay. I think it took an hour or so to walk out to the rock. I can give you directions if you're interested. In the same area, there are some karst formations that are pretty interesting. There's like a small canyon there. By small, I mean around six or eight feet deep. Here's a picture of a more impressive pegmatite boulder from the U.P.  Untitled |
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Post by 150FromFundy on Jun 2, 2014 21:23:09 GMT -5
It's only a cool rock if you can bring it home with you. LOL! Fair to say that one cooled slowly.
Darryl.
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