A REPLACEMENT OF WOOD BY DOLOMITE 



S. F. ADAMS 

 Stanford University 



A score or more minerals are known to have replaced wood. 

 Cases of most . of these types of replacement were recorded by 

 J. R. Blum^ during the years 1847-79. Since 1879 there have 

 been few additions to the list of wood-replacing minerals as given 

 by Blum. To my knowledge, replacement by dolomite has not 

 before been mentioned. For this reason, the accompanying 

 account has been made as complete as possible. 



In the known replacements of wood chalcedony is undoubtedly 

 the most universal petrifying mineral. Fine examples of this kind 

 of replacement are found in the petrified forests of Arizona, where 

 very large tree trunks have been completely agatized.^ Petri- 

 factions of this type come from localities in Colorado, Utah, Cali- 

 fornia, and from the Yellowstone Park. I have at hand an 

 unlabeled specimen of petrified wood which is thought to come from 

 Arizona, in which the wood is largely replaced by quartz. A thin 

 section of this specimen shows anhedral quartz crystals which 

 include sometimes a dozen well-outlined wood cells. The general 

 character of the quartz is similar to that to be described on a later 

 page. Wood opal replacing entire tree trunks is found in Hungary; 

 nor is it uncommon in this and other countries. Precious opal, 

 usually as a late development after common wood opal, is known 

 to come from Australia and from a deposit in Nevada, where the 

 opal is being* recovered for commercial purposes. Blum men- 

 tions opalized wood with an incrustation of hyalite. 



Replacements by calcite and aragonite have been recognized 

 in many places. The strong crystallization of these two minerals 



'J. R. Blum, Pseudomorphosen des Miner air eichs, Nachtrage, i, 2, 3, 4. 

 2G. P. Merrill, "The Fossil Forest of Arizona," Am. Mus. Jour., Vol. XIII, 

 pp. 311-16. 



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