38 
IOWA ACADEMY OF SCIENCE Voi,. XXVIII, 1921 
precipitation of calcium and magnesium carbonates, from which 
he reached the conclusion that dolomite is simply a chemical pre- 
cipitate. This view has not been generally adopted. 
In more recent times, 1909, G. Linck published a report of a 
new method of making dolomite. He mixed solutions of mag- 
nesium chloride, magnesium sulphate, and ammonium sesquicar- 
bonate, and then added a solution of calcium chloride. An amor- 
phous precipitate came down, which on gentle heating for some 
time in a closed tube became crystalline. This had the composi- 
tion and optical properties of dolomite. Linck believes that his 
experiment explains the formation of marine dolomite, and that 
the ammonium salt necessary can easily result from the decompo- 
sition of organic substances. 
The ideal dolomite, CaCOg ‘ MgCOg, would contain : 
PER CENT 
CaCOg 54.35 
MgC 03 45.65 
But such a dolomite is ideal and does not exist in nature. 
The Niagaran dolomite, the formation in northeast Iowa, which 
has, indeed, a wide distribution, being found in many states, is an 
approach to the ideal. The composition of different layers varies, 
but a fairly typical specimen would or might reveal : 
PER CEN*r 
CaCOg 54.35 
MgCOg 43.65 
SiO^ 1.00 
AI 3 O 3 and Fe 303 1.00 
100.00 
We have examined dolomites, so-called, from many different 
countries and find some that are properly termed dolomites, while 
others are magnesian limestones, with only a small percentage of 
magnesium. Some contain very little of either calcium or mag- 
nesium, but are quite pure sandstones. 
I. Specimen from New Almadin, California . — This is a 
hard, greyish- white variety. It consists of large compact crystals, 
with one surface coated with a brown deposit. The specific grav- 
PER CENT 
SiO^ 
0.40 
Fe.O, 
8.57 
AiA 
0.00 
CaC03 
53.58 
MgC03 
37.86 
100.11 
