HOW SAFE IS THE TASTE TEST FOR HALITE?

Introductory geology labs stress simple physical testing (luster, hardness, etc.) to identify common minerals using mineral charts to eliminate minerals not exhibiting a particular property. Special properties (magnetism, specific gravity, taste, etc.) for specific minerals narrows mineral identity. Tasting is used primarily to identify halite (NaCl), but also works for borax (sweet alkaline taste), epsomite (bitter), melanterite (sweet, astringent and metallic), and sylvite (bitter). Students often express safety concerns about licking minerals, especially when they realize others have licked the specimen. Obviously potential poisonous minerals are excluded from laboratories, and instructors generally admonish the student to use the taste test last and only when possible mineral choices are narrowed to those that the test can be safely applied; although, oddly enough, none of the introductory lab manuals checked had warnings regarding safety issues associated with taste testing. As an exercise in medical geology, we cultured microbes from a halite sample used for nearly 25 years and licked by numerous students over that time span, a sample repeatedly licked by only one person, and a commercially purchased unused and freshly exposed surface of halite licked by one person to determine microbial presence, especially those potentially harmful to students applying the taste test. From the new crystal licked by one person, we identified sixteen different phenotypic groups of microorganisms after incubation of the crystal in growth medium. 16S ribosomal RNA sequence analysis was performed on one representative from nine of the sixteen groups. From this analysis, we obtained one Bacillus sp., four Paenibacillus sp., and four Staphylococcus sp., probably Staphylococcus epidermidis. All three genera are gram-positive bacteria, meaning they have a thicker cell wall. Comparing our results to published studies of human tongue biome, we find that all of our cultured microbes occur naturally within a typical person’s mouth and do not pose significant health risk as used in lab. Saliva with microbes can be transmitted as the halite is reused, especially if the test is administered quickly after a previous licking, so caution is warrented, but the process is essentially safe.