Waco Gem and Mineral Club, Waco, Tx

16.5 Collecting Preparing and Storing Thumbnail Fossils


16.5: Collecting, Preparing, and Storing Thumbnail Fossils

Collecting thumbnail fossils. Small thumbnail fossils might be found right on the surface of a fossil locality, having weathered free and mixed in with surrounding soil. To increase the odds of finding specimens, take screens to sift through such soil at the base of a fossil outcrop. You‘ll also find many thumbnail fossils embedded in limestone, sandstone, or shale. Rather than trying to remove fossils from hard matrix in the field, kids should bring those specimens home to work in a more controlled setting with an assortment of tools at hand.

Preparing thumbnail fossils. As with miniatures, preparing thumbnail fossils involves trimming away matrix. Basic supplies needed include: rock- or lapidary hammers and small chisels (along with eye protection); pliers or nippers to snip away pieces of matrix and/or special vice-like rock trimmers; a small rock saw; a regular hand magnifying glass or, better, a bench magnifier that allows you to work with both hands free; Dremel-type bits, saws, and brushes; dental picks; tweezers; and glue. Some small silicified fossils embedded in limestone may be freed in acid baths using acetic acid (vinegar) or muriatic acid (often sold with swimming pool supplies).

Caution: Working with acid should always be done by an adult exercising great precautions with long rubber gloves and aprons, eye protection, and a high quality respirator mask in well ventilated areas, with any open containers kept away from areas where pets might be or where fumes might cause damage to paints, pipes, etc. We do not recommend that kids work with acid of any sort, and any adults electing to do so should first thoroughly familiarize themselves with all procedures and precautions.

Storing thumbnail fossils. Thumbnails are best stored in 1-inch Perky boxes, named after their creator, Willard Perkins. These small plastic boxes, available from mineral suppliers, usually have a black bottom lined with Styrofoam and a clear plastic top. Specimens are often pushed into the Styrofoam or attached to it with a dab of tack. Instead of Styrofoam, you can also use 1-inch acrylic squares that make it easy to remove a specimen from the Perky box for display in an exhibit. For kids just beginning and on a budget, matchboxes will also do, or plastic boxes with compartments and fold-top lids of the sort sold in bead stores or with fishing tackle. The bottom of each compartment should be lined with cotton to keep specimens from rolling about. Basically, use anything that‘s enclosed so as to contain the small specimen securely and to keep out dust.

Note: Kids can use this activity to satisfy requirements toward earning the Collecting badge simultaneously (Activity 5.1).