| From: humbum | 17/06/00
16:03:16 |
| Subject: Finding Shiny yellow metal |
post id:
86086 |
| What if I was digging in my
garden and I find something that catches my eye, so I pick it up and give
it a wipe and find that its a shiny yellow metal. How can I test it on the
spot that it is not fools gold and is really gold
stuff? | |
| From: sam | 17/06/00
16:18:04 |
| Subject: re: Finding Shiny yellow metal |
post id:
86090 |
| My apologies, fool's gold is
pyrite, which is apparently yellowish grey to silver grey. However, gold
has a hardness of 2 1/2 to 3, while pyrite has a hardness of 6 - 6 1/2.
(from http://www.minerals.net/gemstone/gemstone/pyrite/pyrite.htm
. | |
| From: Alan™ ® | 17/06/00
17:22:14 |
| Subject: re: Finding Shiny yellow metal |
post id:
86113 |
| Let's dismiss the mica for
starters. Micas are a group of minerals based around
Si4O10, the most coomon ones are muscovite a
aluminuim, potassium silicate. It appears in sheet form usually and is
transperant in this form. Biotite is the other common one, a Potassium,
magnesium, iron, aluminium silicate. This one appears as black crystals
often. If you own a granite kitchen top, you can see both these minerals
fairly easily. There are a couple of possibilities when it comes to lumps of gold coloured rocks. The two best indicators of gold is it's weight and it's softness. Gold is really heavy, if you have a lump of lead around, ie a fishing line sinker or a balance weight for a car wheel, feel how heavy it is, well gold is 50% heavier again. It's hardness is 2.5 - 3.0, which means that you should just be able to scratch it with your finger nail. Pyrites are much harder, 6.5 - 7.0, so you can just scratch it with a steel knife. Often rubbing a pyrite will remove the gold surface, leaving a dark grey surface. Striking the rock with a knife will cause a spark. Chalcopyrite (copper pyrite) is a softer form 3.5 - 4.0 of pyrite. However it is very brittle, scatching it with a knife will cause it to crumble. The spark test doesn't work for chalcopyrite. | |
| From: sam | 17/06/00
17:44:38 |
| Subject: re: Finding Shiny yellow metal |
post id:
86123 |
| ah well. :) At least I got it
sort of right in the end... although the figures for hardness of pyrite
differed by 0.5 from the figures that you gave and the ones I
did. | |
| From: Alan™ ® | 17/06/00
17:58:39 |
| Subject: re: Finding Shiny yellow metal |
post id:
86129 |
| No you were correct, I misread
the hardness. Mohr's hardness, is a useful tool in the field, but it's really quite inaccurate. At least with metals we have proper calibrated tests (Vickers and Brinnel). Metallurgy has its own field tests, the most interesting one I've come across, it the file test. At Borg Warner, they hardened and softened ordinary metal files and calibrated them. In doing so they could test each axle or gear as it came out of the hardening furnaces. It saved them doing proper hardness tests in the laboratory on each piece, instead they fully tested a couple of pieces each day. | |
| From: Paul S | 17/06/00
21:31:20 |
| Subject: re: Finding Shiny yellow metal |
post id:
86249 |
| All that glitters is not Gold.
actually if it glitters it isnt likely to be. Mica does glitter, pyrites
looks shiny and goldy sort of colour, but only gold looks really yellow,
Have a look at a wedding ring. Malleability is another good test for gold,
have you seen films of those Indian people hammering on a small piece of
gold until they get it tissue thin.(to sell to the devout to stick on the
Budha) | |
| From: kelvin fox | 17/06/00
23:44:16 |
| Subject: re: Finding Shiny yellow metal |
post id:
86294 |
| Hi All Well done guys-between you all you got it right. Density is the big give away, also micas are phyllosilicates-ie flat minerals. This is a dead give away as gold is far "chunkier". Hardness is also a good tool but difficult to assess without an accurate hardness testing kit. Streak is a good one. Rub the suspect mineral on an unglazed porcelain tile. Gold I believe has a gold streak whereas most other minerals don't have a gold streak. maleability is difficult as chunks of gold are difficult to test-you really need to flake some off to test maleability. You really don't want to start beating your newly discovered gold nugget with a hammer. If you suspect a sulphide such as pyrite or chalcopyrite pour a little hydrochloric acid on it. The smell given off will be hydrogen sulphide (rotten egg gas). This will not occur with gold. Colour is not a good indicator as it varies according to the silver content but most gold nuggets I have seen are certainly very golden in colour. Crystal shape is a give away. Pyrite and other sulphides have distinct crystal habits. gold does too but gold crystals are rare and usually small. Hope I have helped in some small way. Kelvin Fox | |
| From: Dr. Ed G (Avatar) | 18/06/00
3:13:42 |
| Subject: re: Finding Shiny yellow metal |
post id:
86351 |
| Chalcopyrite is cool... I bought
a nugget from a store in SanFrancisco to put on my bookshelf. Fabulous
colours!!! The person at the checkout asked me what I wanted it for. I
said 'cause it looked cool. She replied, "you know it has thereuptic
properties!" To which I replied, "Yes, I know, that's what I said, it
looks cool!" I think she thought I was a freak... Kelvin, have you been to the minerology section of the Museum of Natural History in New York? If for whatever reason you get the chance, it's an absolute must... it ROCKS! (pardon the pun :-) | |
| From: kelvin fox | 18/06/00
23:07:37 |
| Subject: re: Finding Shiny yellow metal |
post id:
86617 |
| Hi All Rock coolness aint such a bad property. It is the reason why some people like particular rocks at a mineral sale and some don't. It is such a personal thing. My favourite group of minerals is the zeolite group. When I was at uni my bedroom had my rock mineral and fossil collection in it-over 2000 individual samples-all catalogued. I don't own it any more. I could not bring it to WA when I got married. I donated it to the uni where I studied. I have never been out of Australia but I love museums of natural history. I used to work at the geological and mining museum in Sydney (before the Govt decided the citizens had no need for such a museum) and I was friendly with the mineral curators at The Australian museum so I spent lots of times in the backrooms of each of these fine institutions. The amazing thing was that in the case of each of these museums the best samples were not on display. Thanks for the museum tip. The other ones I want to visit is The Smithsonian and the mineral museum in Paris-reputedly the best in the world. Kelvin | |