WoW! Things To Do
Streak Testing
by Donald Clark CSM

... Streak tests are fun things to do. There are many surprises and you can use them to amaze your friends. It is also very easy and inexpensive.
... All you do is to rub a piece of gem material on a tile and look at the color of the streak it leaves. Here are the details on how to perform a streak test. First, go to a building supply store and buy a ceramic tile. Some tiles have rippled backs. You need to find one that has large flat areas on the back. We use ceramic tiles because they are hard enough that the gems will rub off on them.
... Next, chose your gem materials. (Use rough pieces you have collected, not finished gems. See the warning below.) Rub the material firmly against the back of the tile; you cannot do this on the glazed or shiny side. Now look at the streak it left and see what color it is. That is all there is to it!
... Here are some of the results you can expect. Dark green malachite will leave a green streak. No surprise there. Brown tigers eye leave a streak that is almost the same color as the stone. Again, this is no surprise. Next, test some lapis. This dark blue gem will leave a very light blue streak. Hematite is a dark gray, almost black when whole. Guess what color its streak is? The answer is rust red. You have to see this to believe it! Pyrite, or fools gold, is another surprising stone. This brassy colored mineral will leave a black streak on your tile!
... Now, if your collection contains some pieces of rough amethyst, tourmaline, or other richly colored crystals, give them a test. Almost all of your stones will leave a white or colorless powder.
... When you know the streak colors of your gems, you can put on a magic show for your friends. Arrange your tests so the first stones have streaks close to their natural color. Then move on to the colored stones that leave a white streak. Leave the big surprises, pyrite and hematite, to the end.

... Before testing your stones, ask your friends what color they expect to see. They will usually be wrong and you will delight them with the "magic" results!

Warning! Streak testing is destructive and will damage the stones you are working with. Do not use your mother's, (or anyone else's,) gems. Only preform streak tests with pieces of rough or damaged gems.

Return to W.o.W!