20 Geology of Texas

Friday, 5 April 2013
8:00 AM - 10:30 AM
Amphitheater 204

THE 1928 CLINE, TEXAS METEORITE

Paper number: 20-4
Program: Technical Sessions
Time: 9:00 AM – 9:20 AM

Authors

Abstract

Residents scattered throughout West and South Texas were startled on the cloudless afternoon of June 23, 1928 at 4:40 PM when an exceptionally bright and loud meteor flashed across the sky. The meteor was seen and heard across a region from Roscoe to Sanderson to Brady to Austin to San Antonio to Alice and to Laredo. Fresh recollections of observers were published in the geology literature. Triangularization identified that the fall was within tens of miles of Cline, Texas in western Uvalde County. The meteorite was never located. In 2009, a Uvalde County landowner stumbled upon a large, dark, odd-shaped rock in the vicinity of Cline. Analysis shows that the forty-pound object is a stony-iron meteorite with distinctive atmospheric entry markings along with distinctive, but complex, olivine mineral content. The meteorite has a thick, cup-shaped appearance on the dark, mottled concave surface. The convex surface is dark and grainy with scattered olivine crystals. The broken-cup shape represents perhaps one-eighth of a mantle of a missing spherical core.

A one-inch diameter core was cut through the specimen with a sapphire, water-jet apparatus and examined optically and with TEM. The cut surface of the core shows bulk distribution of sub-millimeter to millimeter inclusions of silicates. The location at the convex end has a high concentration of olivine minerals, many whitish in color. Some larger inclusions are a few millimeters in size. Upon magnification the bulk shows silicates scattered and well mixed within the metal. The olivines show distinctive spheroidal growth patterns. Iron matrices contain a few percent of nickel, chromium and manganese with traces of calcium, carbon, chlorine, aluminum and potassium, strongly dependent on location. The meteorite appears to preserve an intermediate stage of mantle formation from an asteroid.