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astrobleme (ăsˈtrōblēmˌ), large, circular structure ranging from c.1-2 mi to 40 mi (.8–64 km) in diameter. Astroblemes are found at numerous places on the earth's surface, e.g., Meteor, or Barringer, Crater in Arizona, Brent Crater in Ontario, and Vredefort Ring in South Africa. The presence of meteor fragments, strange conical fracture patterns (called shatter cones), and coesite (a superdense, high-pressure form of quartz) in the rocks at astroblemes suggest an impact, rather than volcanic, origin to these circular structures.
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A circular-shaped depression on the earth's surface produced by the impact of a cosmic body.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.