brizzonator
off to a rocking start
Member since July 2020
Posts: 23
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Post by brizzonator on Aug 5, 2020 9:02:52 GMT -5
Good morning, first, I am a complete newbie to rockhounding and tumbling, but it has seriously taken up my interest, so I am trying to learn all I can.
The main questions I have are concernig the MOHS hardness measuring. 1. If a stone has impurities or has been river-tumbled, does that effect the hardness any? I guess, is their any wiggle room in it? 2. Can you advise me what a really good field guide to minerals is? I am rockhounding primarily in SE Texas.
3. The thing that confused me was I found in a local river bed near Houston, the following stones (going to try and attach pics). Both are translucent. The photos I am going to (try and) attach are of them side by side and with a high powered flashlight held undder them in a lit room. When I hear translucent I always think quartz. But I tried scratching one stone with another and they both scratched each other(which made me think, "ok, maybe like scratches like, i.e. only a diamond can scratch a diamond). Then I used a steel knife(just a kitchen steak knife) because online it said that was less hard than quartz. Looked like a scratch. Then with a penny, looked like a scratch. Then with my nail, looked like a scratch. But when I just now(sorry the last photo is not so clear) trained the flashlight on the yellowish one, I just now noticed that the "scratches" looked silvery and coppery reflective. So, am I right in assuming that I was not scratching the stone, but only abrading the m,aterial I was scratching with onto the surface of the rock?
Sorry these are newbie questions, but that's what i am, and (at 57) have recently realized I have a heck of a lot to learn about minerals.
Thanks for any advice or teaching! Brian
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stonemon
Cave Dweller
Member since January 2017
Posts: 1,024
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Post by stonemon on Aug 5, 2020 9:21:18 GMT -5
Good morning and welcome to the forum!
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brizzonator
off to a rocking start
Member since July 2020
Posts: 23
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Post by brizzonator on Aug 5, 2020 9:33:34 GMT -5
Thanks!
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stonemon
Cave Dweller
Member since January 2017
Posts: 1,024
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Post by stonemon on Aug 5, 2020 12:00:40 GMT -5
Both of your rocks appear to be silica of some sort and would have a hardness of around 7 mohs. It would make sense that the knife and penny left metal on them and also that they would mark each other.
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Post by rmf on Aug 5, 2020 13:54:40 GMT -5
Good morning, first, I am a complete newbie to rockhounding and tumbling, but it has seriously taken up my interest, so I am trying to learn all I can.
The main questions I have are concernig the MOHS hardness measuring. 1. If a stone has impurities or has been river-tumbled, does that effect the hardness any? I guess, is their any wiggle room in it? 2. Can you advise me what a really good field guide to minerals is? I am rockhounding primarily in SE Texas.
3. The thing that confused me was I found in a local river bed near Houston, the following stones (going to try and attach pics). Both are translucent. The photos I am going to (try and) attach are of them side by side and with a high powered flashlight held undder them in a lit room. When I hear translucent I always think quartz. But I tried scratching one stone with another and they both scratched each other(which made me think, "ok, maybe like scratches like, i.e. only a diamond can scratch a diamond). Then I used a steel knife(just a kitchen steak knife) because online it said that was less hard than quartz. Looked like a scratch. Then with a penny, looked like a scratch. Then with my nail, looked like a scratch. But when I just now(sorry the last photo is not so clear) trained the flashlight on the yellowish one, I just now noticed that the "scratches" looked silvery and coppery reflective. So, am I right in assuming that I was not scratching the stone, but only abrading the m,aterial I was scratching with onto the surface of the rock?
Sorry these are newbie questions, but that's what i am, and (at 57) have recently realized I have a heck of a lot to learn about minerals.
Thanks for any advice or teaching! Brian
In nature there is always wiggle room. Mohs scale of hardness is a relative scale of hardness not an absolute hardness. the hardness from Talc to Corundum is smaller than the hardness difference than the hardness from Corundum to Diamond. mineral inclusions can affect the hardness. weathering affects hardness that is why the suggest using a fresh break. the environment in which the mineral forms can affect the hardness. The images you attached look like quarts (white) and agate (brown) They should have about the same hardness but not the same toughness. Agates can take more pounding before shattering than simple quartz because of the differences in crystal structure. Yes if copper was on the stone the stone scratched the copper.
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brizzonator
off to a rocking start
Member since July 2020
Posts: 23
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Post by brizzonator on Aug 5, 2020 13:58:54 GMT -5
Thanks all, any advice on a good field reference?
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kyoti
has rocks in the head
Member since June 2020
Posts: 542
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Post by kyoti on Aug 5, 2020 20:18:46 GMT -5
If a penny and your nail scratched them, they could be calcite. Calcite looks a lot like quartz but it's very soft. Does if fizzle if you put a drop of vinegar on them?
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Post by Mel on Sept 11, 2020 18:48:47 GMT -5
Second the vinegar test; calcite will fizz just a little bit. The one looks like calcite to me, and the other quartz/ite.
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Post by knave on Sept 11, 2020 20:22:58 GMT -5
Yeah mohs not a linear scale and I’ve seen quite the variance in hardness in amethyst for instance
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Post by pauls on Sept 11, 2020 21:31:42 GMT -5
What they said. Also the hardness can be different depending on the crystal axis, Diamond is actually one that is harder than Diamond on some crystal faces.
Usually a hardness test is more accurate for a mineral. Rocks can be varying amounts of different stuff stuck together. So for example sandstone could be pure Quartz sand so theoretically it should be 7, but if it's only loosely stuck together it can be so soft it falls apart in your hand.
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