How to Test Quartz Hardness Using the Acid Test


The acid test tests minerals for the presence of calcium carbonate. Minerals containing calcium carbonate are generally quite soft, as rated on the Mohs hardness scale. This test can be very helpful in determining if your transparent crystal is quartz or some mineral masquerading as quartz. Since quartz is about a 7 on the Mohs hardness scale and calcium carbonate is about a 3, the acid will react much differently to quartz than to calcium. You can easily perform this test at home with a little apple cider vinegar.

Things You'll Need

  • Unidentified minerals
  • Glass casserole dish
  • Apple cider vinegar
  • Small bowl
  • Eye dropper
  • Place your minerals in a glass casserole dish, spacing them about 2 inches apart. Make sure the dish is squeaky clean. Your minerals should also be free of dirt, grime or dust. Rinse and dry them gently before arranging them. Arrange the minerals you think may be quartz on one side of the dish and other minerals on the other.

  • Pour a little apple cider vinegar in a small bowl. Place the tip of your eyedropper in the vinegar and squeeze the bulb to suck up some of the vinegar. Don't let the vinegar bubble up into the bulb; it could damage the rubber. Fill the dropper about halfway; that should be plenty.

  • Drip a single drop of vinegar onto your first specimen. If it fizzes, it contains calcium carbonate and is not quartz. If it does not fizz, dry the specimen and repeat the test. If it still does not fizz, it does not contain calcium carbonate and is likely quartz.

  • Drip a single drop of vinegar onto different parts of specimens containing different colors and textures. These specimens may contain several different minerals. Quartz often mixes with other minerals, so you may have pieces that are part quartz and part something else.

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  • Photo Credit pyrite quartz image by A74.FR Ben Fontaine from
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