350 
IOWA ACADEMY OF SCIENCE Voe. XXIX, 1922 
inger that this reaction accounts for the frequent association of 
gypsum with dolomite. 
T. Sterry Hunt conducted a long series of experiments on the 
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 magnes- 
ium chloride, magnesium sulphate, and ammonium sesquicar- 
bonate, and then added a solution of calcium chloride. An amor- 
phous precipitate came down, which on being gently heated for 
some time in a closed tube became crystalline. This had 1 the 
composition 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 
decomposition of organic substances. 
An ideal dolomite would consist of calcium carbonate 54.35 per 
cent, and of magnesium carbonate 45.65 per cent. Possibly such 
a dolomite has never been found as produced by nature and may 
not exist. The calcium carbonate or magnesium carbonate or 
both may be partly replaced by different substances, especially by 
silica, iron and alumina. 
The rock formation of northeast Iowa is dolomite and fairly 
typical. The analysis of a specimen from near Mount Vernon, 
Iowa, resulted as follows : — 
PER CENT 
Si0 2 0.86 
Fe 2 0 3 and Al 2 Os 1.14 
CaCOs 54.35 
MgCOs 43.65 
Total 100.00 
Analyses are here given of specimens from the Austrian Tyrol, 
the locality where Deodat Dolomieu first studied dolomite rocks 
and made known their composition. 
1. Specimen from Martinswand, Tyrol, Austria. This is a 
compact, crystalline, greyish- white variety. 
Si0 2 . . . 
Fe 2 0 3 . . 
AkOs . . 
CaC'Os . 
MgCOs 
Total 
PER CENT 
. 1.10 
. 1.70 
. 0.00 
. 49.71 
. 48.53 
.100.04 
This is a fairly typical dolomite although the magnesium car- 
bonate nearly equals in amount the calcium carbonate. 
