BASALT GRINDSTONE FRAGMENTS FROM THE KARAK PLATEAU REGION OF CENTRAL JORDAN

Seventeen basalt grindstone fragments collected from sites within the Karak Plateau region of Jordan were examined using hand-specimen, petrographic, X-ray diffraction, and X-ray fluorescence techniques. These implements exhibit many of the physical, microscopic, mineralogical, and chemical properties exhibited by basalt samples collected from flows near the archeological sites examined here; however, one basalt fragment is quite different in appearance and composition (especially its high alkali content) and may have come from basalt flows closer to the Dead Sea.

Most of the grindstone fragments are vesicular or amygdaloidal with calcite as the dominant mineral filling the voids. The major minerals present are olivine (with iddingsite rims), plagioclase (anorthite contents range from An62 to An65 for the phenocrysts and An60 to An62 for the matrix plagioclase), clinopyroxene, magnetite, and apatite. Glass is present in some samples. Like most basalts in the region, the grindstone fragment compositions plot in the tephrite-basanite and basalt fields. Trace element data were used to prepare tectonomagmatic discrimination diagrams. A ternary plot of the concentrations of niobium, zirconium, and yttrium reveal that the sample compositions plot in the "within-plate alkali basalt" and "within-plate tholeiite" fields. Chemical data suggest that the basalts were derived from partially differentiated primary melts that ascended rapidly, avoiding significant crustal contamination.

Differences in composition and physical features suggest that the acquisition of basalts for preparing such implements was essentially random; however, some may have been introduced into the Karak region through normal trade and migration, etc. Archeological studies in the Karak Plateau region are urgently needed because rapid population growth and economic development in this part of Jordan are destroying many sites.