Past Cobb-L-Stones Articles

The fact that Alabama has been blessed with a unique type of petrified wood is not generally known in rockhound circles.

There are two general areas where the unique type of wood covered with quartz crystals is found. One is near Wetumpka in Elmore County and the other is near Brilliant in Marion County. Both sites are on private property. There are some indications of other scattered sites of similar wood but these two will be addressed separately.

The Marion County exposure is about 50 feet above the coal deposit which has been strip mined. Current estimate is that the trees are float laid down in the latter part of the Pennsylvanian period and prior to the general crustal upheaval of the area. Subsequent to deposit, the logs were all encased in a ferrous sandstone varying from ½ to 6 inches in thickness. Prior to the petrification process most of the cellulose wood fibers had rotted and remain as a clay-like filler material. The molecules of cellulose remaining were replaced with SiO₂, i.e., petrified. Either concurrently or subsequent to this process, the presence of a super-saturated solution of SiO₂resulted in all of the petrified wood surfaces being covered with small (micro to 5mm) quartz crystals. Even minute separated pieces of wood were petrified and covered with crystals. Unknown temperatures and pressures may have influenced this process. Each phenomenon make the wood of interest to most. The microcrystals – free and formed in the clay – are especially well crystallized and provide nice specimens for micro-mounts. The smoky crystals make particularly nice specimens as dazzling surfaces on petrified wood. Photographs cannot do justice to one of these specimens – neither can my vocabulary.

The Elmore County exposure resulted from Alabama Power Company digging a cut-off canal on the Coosa River. Generally, about 30 feet below the current land surface, the petrified logs were part of the excavated material. Water level in the canal is such that access to the exposure is only possible when the lower lake is low and turbines above are not running. The wood is located about 15 feet below normal water level.

This deposit has quartz crystals similar to those at the Marion County site but there are major differences in the two exposures. The crystals vary in size from micro to 15 cm in length. All are doubly terminated even though attached to the SiO₂wood. Colors of the crystals vary from a brilliant clear through all phases of smoky to an opaque black. Crystal arrangement also varies from single to multiple overlapping arrangements. Like the Marion County specimens, football, shaped clusters are found in the clay-like wood residue. The principle difference between the two sites is a clay-like red material. At the Elmore County site it is carbonized wood. The petrified wood is generally black to gray but this filler material is really charcoal. When it is heated it will burn. The clusters and individual clear quartz crystals are in this charcoal.

(Note: This was the prize-winning article both in the American Federation and Eastern Federation bulletin contest of 1975. Mr. Watts was the past President of the Huntsville Gem and Mineral Club.)