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I.—The Mineral Condition of the Calcium Carbonate in Fossil Shells

Published online by Cambridge University Press:  01 May 2009

Grenville A. J. Cole  and
Otway H. Little
Grenville A. J. Cole
Affiliation:
Royal College of Science for Ireland.
Otway H. Little
Affiliation:
Royal College of Science for Ireland.
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Extract

A recent paper by Mr. A. R. Horwood on “Aragonite in the y Middle Lias” raises again the question of the condition of the calcium carbonate in fossil shells. Mr. Horwood speaks (p. 176) of Jurassic shells as being “preserved in aragonite”, and quotes Dr. Sorby as being of the same opinion. But is Mr. Horwood sure that his shells are still in the aragonite condition? Sorby, when he writes of “aragonite shells”, means as a rule shells that were formed of aragonite at the time of the death of the originating animal; but he describes how, in many of our fossiliferous rocks, such shells are represented either by hollow spaces or by pseudomorphs in granular caleite. He points out that oolitic grains, originally consisting of aragonite, have similarly been changed into calcite, the more stable form of calcium carbonate. Some oolitic grains, however, were thought by him to have consisted of calcite from the outset. Doelter, after summing up Linck's researches on calcite and aragonite, states that calcareous oolites now consist of calcite; and we have no doubt that the “recrystallized aragonite concretions”, quoted by Mr. Horwood from Sorby, were held by Sorby to be at the time of examination in the calcite state.

Type
Original Articles
Information
Geological Magazine , Volume 8 , Issue 2 , February 1911 , pp. 49 - 55
Copyright
Copyright © Cambridge University Press 1911

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References

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