FMF - Friends of Minerals Forum, discussion and message board

[Idahorocks]

The other day I decided to use my good ol' standby "The Ice Test method" once again, to find out if this new specimen of Malachite I just got in was or wasn't the real thing tee he...
Anyway. Yep!! It did not melt the ice. So I'm figuring (remember my lack of education) that it's probably the real thing. I went to my other Malachite stones to test them. All of the natural looking ones I have did not melt the ice. But one I was sure was Malachite did. hm... I could not figure this out. It certainly looks right, but it's polished not natural. Anyone got any feedback for me?

Darlene

[alfredo]

What is the "ice test method"?

[John S. White]

Glad Alfredo raised that question, I have no idea what the ice test is.

[Idahorocks]

Hello Alfredo,
The ice test method (I learned from a pond shop, when I asked about diamonds and how to tell if they were real or glass) is to place the minerals on frozen water. If it melts, it is mineral : ) This does not work with amber, plastic or glass, and apparently not some malachite. For Malachite has a mineral impostor called pseudomalachite. Apparently Malachite is different, but I've yet to discover how. One test to tell would be the acid test which you would be able to tell by the Characteristics of malachite would appear: Weakly effervesces in acid. And now after reading what you had to say about citric acid. I think I may find out at last. I've still got to do research on Malachite. Isn't it funny. One goes through life loving a particular gem, and not knowing what it's. Please forgive my ignorance but, The say: Rocks are made of minerals. For example, the igneous rock basalt, which makes up most of the Earth's oceanic crust, but I'm just learning, I saw this info on a website. I'm so thankful for the internet it brings life to ones existence.
Thanks for asking...
Darlene

PS. I have to run, please forgive me I am unable to read through this again. To make sure I've not left out wording or such. Please bare with me at this time If I have. Darlene

[Les Presmyk]

I would not place any acids on your malachite, especially if they are polished and in jewelry. This will result in dulling the surface and the only way to bring back the shine will be to have it polished.

Pseudomalachite is much less common than malachite and looks very much the same. I would consider it more desirable, as well. This is the first time I have heard of this ice test and someone more knowledgeable than I will have to authenticate it or declare it an old wive's tale.

Malachite or pseudomalachite will always be heavier than plastic. Hardness is another test that can be made on the back of the stone.

[alfredo]

OK, now that Darlene has explained the method, the test makes sense; it's not superstition. What one is actually detecting is the heat storage capacity of the material and its thermal conductivity. Put a warm rock on the ice and it will transmit its heat to the underlying ice. Would work very well in the case of diamond (assuming the diamond is significantly warmer than the ice to start with; a cold diamond isn't going to melt any ice).

In the case of malachite, I assume we're talking about "pseudo (as in fake) malachite", malachite powder held together with a resin or plastic (low thermal conductivity), and not the mineral species pseudomalachite. The plastic or resin would reduce the heat transfer, so the ice wouldn't melt.

[Pete Modreski]

It makes sense (I've never heard of doing this, but it does make sense, as Alfredo says, at least in theory.) This is the reason that most natural minerals will feel somewhat cold to the touch, and amber or plastic will feel relatively warm; and that a diamond (at any rate, one large enough to really feel its surface--which is not often that most of us handle diamonds large enough to sense this) would feel especially cool, and hence that diamonds are referred to as "ice".

Of course, these heat-sensing tests all assume that the stone in question is at "ordinary cool room temperature", so one's fingers can sense the difference between body temperature and that of the stones. To do the "ice melting test", one would have to assume that the stones were at ordinary room temperature to begin with. No doubt, the "ice test" would work best with a reasonably large piece of a slab or cabochon, and not very well with a tiny cut stone.

We all often do this casually by just feeling the stone; most natural rocks and stones feel cool to the touch for this heat-transfer reason, whereas any plastic-based synthetics would likely feel warm, or at least, "not cool", and would make one suspicious about their authenticity. Their feeling "warm", would go along with their feeling unusually light in weight too.

Pete