Stones and minerals that are sufficiently beautiful, durable, and rare are known as gemstones. A gemstone with only one of these qualities is less desirable than one with all three. For example, a stone with rich color but not sufficiently durable to withstand daily wear in rings finds little favor as a gemstone except in brooches or pins where the stone is relatively safe from abrasion. Likewise, a stone that is beautiful and durable may be of little interest as a gemstone because it is commonly found in great quantities.

The departure point of the Villa Capri Motor Hotel may be gone, but the geologic information within Guidebook Number 3 remains relevant to this day:  "The four stops of this field trip are in the Upper Eocene (Jackson) and Oligocene volcanic ash and bentonite beds, which crop out about 50 miles southeast of Austin. In the road log, the geology of the area between Austin and these volcanic beds is only briefly noted.