tuff

tuff

a rock formed by the fusing together on the ground of small rock fragments (less than 2 mm across) ejected from a volcano

Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005

tuff

[təf]

(geology)

Consolidated volcanic ash, composed largely of fragments (less than 4 millimeters) produced directly by volcanic eruption; much of the fragmented material represents finely comminuted crystals and rocks.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

tuff, volcanic tuff

A low-density, high-porosity rock; composed of volcanic particles, ranging from ash size to small pebble size, which are compacted or cemented together; sometimes used as building stone or as a thermal insulation material.

McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.