markward
off to a rocking start
Member since December 2006
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Post by markward on Feb 11, 2007 9:40:57 GMT -5
Hi anyone help with these two The first two pictures are of a Blue rock which a knife, file & glass does not scratch. Obvious banding and looks similar to quartzite. They do form a flash when stiked together in the dark The second one is a very soft rock (some sort of Coral crystallised into calcite or similar) It has a muscovite sheen to it. Apologies for the poor photo's but ithink i need to invest in a better camera soon. Here is a better picture of it i hope!
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Sabre52
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Me and my gal, Rosie
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Post by Sabre52 on Feb 11, 2007 12:24:19 GMT -5
Tough with those pics but the first does look like quartzite and the second kinda looks like selenite ( gypsum) crystals...mel
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markward
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Member since December 2006
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Post by markward on Feb 11, 2007 15:28:41 GMT -5
Would it at all be possible for the blue rock to be a Quartz Schist as it is lighter in weight than normal quartz/quartzite and hardness about 7
Also the second one which you say may be selenite does not react with hydrochloric acid..is it normal for some sort of coral plant to turn into this..this speciman comes from Cyprus
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Sabre52
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Post by Sabre52 on Feb 11, 2007 16:20:54 GMT -5
Mark: I'm more of a quartz mineral guy and those were only guesses based on your pics. Tough to ID those sorts of materials without having the sample in hand. Shistose rocks are very sparkley from the mica contained in the specimen. Is yours sparkley? If so shist is a good bet. The second specimen is definitely not calcite or gypsum then as both would react with the acid. If it's pretty heavy, barite would be a possibility as it is not soluble in acid. Coral (animals, not plants) are usually replaced by either calcite or silica. I have seen barite wood though so it can replace organic lifeforms. I suppose theres a possibility to have coral replaced by barite but there are crystal structures that are coral like without being of organic origin...mel
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markward
off to a rocking start
Member since December 2006
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Post by markward on Feb 11, 2007 16:50:09 GMT -5
Thanks Sabre, the quartz has no mica, so ruling out a schist (i didn't realise that schist always contains mica) so is probably quartzite ...but it seems a very light-weighted gritty/sandy rock
The second coral rock is very soft ie scratch with finger nail .
Understandably very hard to ID when not having a sample to handle but this is the subject i get very frustrated at when i have some rock and i wish to put a label on it..i get very confused..and do really appreciate all the help you give.
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Sabre52
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Me and my gal, Rosie
Member since August 2005
Posts: 20,466
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Post by Sabre52 on Feb 11, 2007 20:25:54 GMT -5
Mark: I believe there are non mica shists. Shists are generally sparkly due to the presence of foliated crystal structures. Most of what I see out here are mica shists but I think there are also chlorite, hornblende, epidote and talc shists and probably others too. As I've said, I'm many years away from college geology and minerals are really not my thing *L*....mel
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stefan
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Post by stefan on Feb 12, 2007 11:50:59 GMT -5
Not to critize- but if you move the camera back a bit I think the pix will come out better- I noticed in the last picture the Bag of rocks in the background was very clear!!! It looks like Gypsum Crystals to me- very nice ones to boot (we get a lot around here too- but they are usually massive and unremarkable) On the first pictures- looks like a quartzite- Maybe a schist or a gniess- but based on the scratch tests you have done I would think it will tumble very well- We get some Banded semi-morphed Quartzites around here- they tumble very well and take a decent shine-
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markward
off to a rocking start
Member since December 2006
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Post by markward on Feb 12, 2007 15:16:28 GMT -5
Thanks Stefan ,advice taken so heres another pic.. If it was Gypsum crystals it would react with hydrochloric acid wouldn't it, and the blue quartz i banged together in the dark last night and they sparked confirming quartz..can't wait to tumble, but like everything else i've got it, has to join the queue. just invested in a larger tumbler..
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