Good agatized wood has been found in and near Palo Duro Canyon, Armstrong County, about 50 miles southeast of Amarillo. Large trunk sections are not uncommon, but most of the material of cutting quality is obtained from small fragments. The Palo Duro Canyon fossil wood greatly resembles the famous Arizona Petrified Forest wood but is not nearly as plentiful. The Palo Duro wood contains yellow, brown, red, and bluish colors most commonly. Some of the wood-producing area is within Palo Duro Canyon State Park which is, of course, closed to collecting. The surrounding area has been worked diligently by local collectors, but new pieces of wood are exposed after heavy rains.
Webb and Duval counties have also produced some good fossil wood specimens.
Gadolinite
Composition: Be₂FeY₂Si₂O₁₀. (Various other rare-earth elements may substitute into this mineral structure.) Crystal system: monoclinic. Hardness: 6.5 to 7.0. Specific gravity: about 4.2. Luster: vitreous to greasy. Color: black; in thin splinters dark bottle green. Streak: white to greenish. Cleavage: none. Fracture: conchoidal to splintery. Tenacity: brittle. Diaphaneity: opaque to subtransparent in thin pieces. Refractive index: variable, about 1.77 to 1.82.
Gadolinite as a cut gem is not seen outside of large collections; however, it can be faceted into black opaque stones of little beauty but of great interest to collectors. The best known locality of this mineral in the United States is Baringer Hill, Llano County, Texas. Unfortunately, this locality was completely flooded by the completion of Buchanan Dam in 1938. Masses and rough crystals of gadolinite weighing over 100 pounds were mined from this locality. The gadolinite occurred in a large, very coarse-grained pegmatite dike associated with quartz, microcline, and fluorite, as well as allanite, fergusonite, nivenite, cyrtolite, thorogummite, and various other rare minerals. Some of the minerals in the dike occurred in very large masses. One quartz mass over 40 feet in diameter was noted, and microcline masses up to 30 feet in diameter were not uncommon. Much of the gadolinite was used by industrial firms as a source of thorium compounds, although some specimen and gem material found its way into museums and private collections. Because the locality was worked mostly from 1910 to about 1925 and because since 1938 the waters of Lake Buchanan have completely flooded the entire area, material from this locality is now exceedingly difficult to obtain. The collection of the Smithsonian Institution, Washington, D.C., contains a cut and polished gem of Baringer Hill gadolinite that weighs 8.6 carats. This mineral is radioactive because of the presence of uranium, thorium, and other rare radioactive elements.
Garnet
The garnet group of minerals is variable in composition. Listed below are the pure members of this group, but garnets found in nature are usually a mixture of two or more of these end members.
Aluminum garnet— Grossularite (calcium-aluminum garnet), Ca₃Al₂(SiO₄)₃ Pyrope (magnesium-aluminum garnet), Mg₃Al₂(SiO₄)₃ Almandite (iron-aluminum garnet), Fe₃Al₂(SiO₄)₃ Spessartite (manganese-aluminum garnet), Mn₃Al₂(SiO₄)₃ Iron garnet— Andradite (calcium-iron garnet), Ca₃Fe₂(SiO₄)₃; may contain magnesium, titanium, and yttrium Chromium garnet— Uvarovite (calcium-chromium garnet), Ca₃Cr₂(SiO₄)₃
Since almandite is the only variety of garnet known to occur commonly in gem quality in Texas, the following properties are for almandite except where noted.
Crystal system: isometric (all varieties). Hardness: about 7.5. Specific gravity: 4.25. Luster: vitreous to resinous. Color: red, deep red, and brownish red (other varieties also yellow, white, orange, pink, black, and green). Streak: white. Cleavage: none. Fracture: subconchoidal to uneven. Tenacity: brittle to tough. Diaphaneity: transparent to subtranslucent. Refractive index: about 1.83.