Mineral specimens that are used properly in the science classroom or laboratory will need to be replaced frequently. Students will be investigating them with hardness tests, streak tests, acid tests and other experiments. All of these tests damage the specimen and make it less fit for the next group of students. To keep the acid…

Hydrochloric acid diluted to a 10% solution cannot be purchased in most communities. The best place to purchase commercially prepared solutions is from a laboratory supply company. Purchasing it ready-for-use is the recommended way to obtain it. Don’t try to prepare your own solution if you don’t know exactly what you are doing and have…

The type of bottle selected for dispensing the acid is important. Laboratory supply stores sell bottles that are designed for dispensing acid one-drop-at-a-time. The lid is always on these bottles (except when they are being cleaned or refilled), and they do not produce a spill when they are knocked over. Bottles with a removable lid…

Most students are intrigued with the acid test and want to try it. To limit frivolous acid use, students should be instructed to use a single drop of acid for the test and to only test specimens when carbonate minerals are suspected. If that is not done, some students will use the acid frivolously. This…

When students are given minerals to identify, two situations can cause problems with their work. 1) In mineral identification labs, some students are ready to call any mineral that produces an acid reaction “calcite” or another carbonate. However, calcite is a ubiquitous mineral and it is often present as an intimate part of other mineral…

LIMESTONE, DOLOSTONE, AND MARBLE Some rocks contain carbonate minerals, and the acid test can be used to help identify them. Limestone is composed almost entirely of calcite and will produce a vigorous fizz with a drop of hydrochloric acid. Dolostone is a rock composed of almost entirely of dolomite. It will produce a very weak fizz when a drop of cold…

Careful observation is important because some carbonate minerals react vigorously and others barely react with cold acid. The carbonate mineral that is most commonly encountered by geologists is calcite (CaCO3). Calcite is a “ubiquitous” mineral. Ubiquitous means “found everywhere.” Calcite occurs in igneous, metamorphic, and sedimentary rocks and is the most commonly encountered carbonate mineral. If you place one…

Carbonate minerals are unstable in contact with hydrochloric acid. When acid begins to effervesce (fizz) on a specimen, a reaction similar to the one shown below is taking place. On the left side of this reaction, the mineral calcite (CaCO3) is in contact with hydrochloric acid (HCl). These react to form carbon dioxide gas (CO2),…

To most geologists, the term “acid test” means placing a drop of dilute (5% to 10%) hydrochloric acid on a rock or mineral and watching for bubbles of carbon dioxide gas to be released. The bubbles signal the presence of carbonate minerals such as calcite, dolomite, or one of the minerals listed in Table 1. The bubbling…