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Generalnon carbonate coating on quartz

16th Jul 2015 08:04 UTCReinhardt van Vuuren

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Hi, at one of my local beaches I found this crystal I extracted from a pocket that I discovered, it has a coating on it that supperficailly resembles a calcite coating to the naked eye but I have soaked it in warm hydrochloric acid with no effect, any thoughs on what it could be? it does seem hard so it could be silica but why would such a coating form?

17th Jul 2015 07:13 UTCsteven garza

Dear Reinhardt;


MORE clay inclusions.


Your friend, Steve

17th Jul 2015 14:45 UTCReinhardt van Vuuren

This coating is hard and above the surface though? could it still be clay? or are you sugesting that there is a layer of silica on top of the main crystal that has the clay included in it. also do note that this specimen was found in a totally different location from the other two specimens.

17th Jul 2015 15:53 UTCTony Charlton

It could be a mineral growth over the quartz that formed because of the proximity to the water source and the dissolved minerals in the water. (note that the pocket did not need to be submerged for this to accrue.) It is also possible that it is clay inclusions in the last layer of the quartz, or a feldspar/minral growth/coating on the crystal.

18th Jul 2015 22:42 UTCsteven garza

Dear Reinhardt;


Is porcelain soft? That's only made of clay. If the last solution sequence had clay, with a tiny amount of silica, then the finished product would be mostly clay clay with just a bit of quartz to give you a false hardness; however, since the coating has an earthy luster, I'm thinking you didn't scratch ONLY on the "chalky" areas, or, you did the test wrong. This has been the case, MANY times; so, use just a POINTY SLIVER of chipped off quartz, against an area that appears earthy/chalky, & see if you get different results, then. I'm betting it'll scratch, even if some quartz is intermixed. When you use a piece of tester material that's as/much larger than sample testing, you tend to override surfaces you intend to scratch, or, you rub a smooth surface over the area, which will leave no scratch.


Please give it a try & let us know the results.


Your friend, Steve
 
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