The Sphere

A short while ago, I purchased a sphere at a yard sale. I could tell by its feel that it was not plastic, and was most likely either quartz (rock crystal) or glass. I sent out a message to some of the mail lists that I belong to, hoping that someone would have some quick and easy suggestions to accurately determine whether the sphere was quartz or glass. They quickly responded with ways to differentiate between the two.

I decide to experiment today to find my answer. It's pouring heavy rain out there. I grab a jacket, the sphere and a few notes. I head out to the "workshop". First thing I do is take off the wet jacket, and hang it to dry. Let the testing begin.

Hardness. Sounds pretty simple. A steel file should scratch glass, but not quartz. If I can only find a file. I search for about five minutes and finally find one. It doesn't seem to make a scratch, so I'd like to say it is quartz. Just the same, I'll feel better doing a bit more.

Density. Not a definitive test, but figured it was a good starting point. The specific gravity of quartz is about 2.65. Glass can vary, I'm told, from about 2.4 to 2.8. The other factor is I may not have an extremely accurate measurement here either, so if the answer shows close to quartz, it may not be a definite proof. But I'd guess a high or low density would dismiss the sphere as glass. I need my ruler to measured the diameter. Another trip in the rain and back. I need a calculator. Okay, the diameter seems to be about 4.3 cm, perhaps a tad less. The mass came to 106.4 grams. I need a calculator another trip in the rain and back. The density came to about 2.6. I felt my accuracy range allowed me to say it might be quartz and continue.

Inclusions and fractures. I'm told that glass would have no visible inclusions or fractures, or perhaps round bubble. Quartz could have inclusions and fractures in straighter or more jagged shapes. I decide to use my loupe, but it is nowhere to be found in the workshop. Yet another trip into the rain that got even heavier and back again. The sphere did indeed have some of these fractures. So now I'm reasonably sure it is quartz. I decide to do one last test, to make a definitive decision, in case.

Ultraviolet light. Short wave ultraviolet light will travel through quartz, but not through glass. I had to get a ladder to climb up high and unplug my ceiling lights, something I didn't feel like doing after my three trips out in the rain. I did it any way, and found this experiment to be a lot of fun and rather fascinating. I brought out a piece of scheelite that glows a bright blue, but only under short wave ultraviolet light. I shine my UV lamp on it. Hello there all happy and bright. I take a piece of glass closest to the size and shape of the sphere that I can find. The stone no longer glows, only appearing its normal gray since the class filters those short wave rays. I then take the sphere and move it eclipsing the UV lamp, as the glas did. The scheelite glow its bright blue.

So I feel that I can say that the sphere is quartz. Yay!

I also took a sphere that I bought several years ago, and ran it over the UV lamp with the same results. I'm really happy with my results, even though I do see that I need to be more organized. But for now, I just need to wait for my jacket to dry out!