That's the way I've always known it.

white tufa-encrusted boulders near the south- ... white tufa were much cooler (37
to 49°C) than ... greasewood and in a nest in white tufa, would ...
elibrary.unm.edu/sora/Condor/ files/issues/v089n04/p0850-p0862.pdf - Similar pages

The Building Stones of Rome
... for instance, in Campania, red and black tufas; in Umbria, Picenum, and Venetia,
white tufa which can be cut with a toothed saw, like wood. ...
www.unc.edu/courses/rometech/public/content/ quarries_and_stoneworking/TheBuildingStonesOfRome.htm - 6k - Cached - Similar pages

Photo gallery, nature photography, black and white photography ...
... This image contrasts the rugged off-white tufa against the rich, blue water and
sky. The original photo was taken with a Nikon 8008 35mm film camera. ...
209.118.37.204/gallery/product1.cfm?CustomerID=517135& ACBSessionID=uI5GLcAZmydqhS71eGqv&SID=1&...


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Note added at 34 mins (2005-10-23 22:11:41 GMT)
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Tuff is volcanic in origin. Tufa is a form of limestone (calcium carbonate).