Dolomite mineral occurs in Missouri as a constituent of dolomitic
limestone or as a vein and cavity filling in the rocks of the Joplin
mining district and as a lining in cavities in the dolomitic limestones
of the southern and eastern parts of the state.
Dolomite when _powdered_ (by scraping the surface of the specimen, for
dolomite is softer than steel or glass) effervesces freely in cold
dilute hydrochloric (muriatic) acid, but the lump dolomite effervesces
_very slowly, if at all_. Calcite effervesces freely in the lump with
cold dilute acid. This acid test is the one certain test for dolomite,
and works with the thick-bedded formations as well as with the showy,
crystal-faced material from veins. See page 11.
Dolomite crystals have a pearly luster and are usually pale pink in the
Joplin district. Their faces are commonly curved but where broken show
glistening to pearly cleavage faces. These properties assume more
significance in mineral determination as one becomes familiar with
mineral collections, but the non-technical person can rely on the acid
test.
[Illustration: Typical dolomite crystals from Joplin region.]
With the above information in mind, one may proceed with certainty to
identify a layer of dolomite from a quarry or hillside, or a crystal of
it in a hand specimen. First, determine that it is scratched readily
with a knife blade or iron nail. Anything too hard to be scratched by
steel is neither calcite nor dolomite. Second, scrape a small mound of
powder on the lump specimens. Third, apply one or two drops of cold
dilute acid to the lump near the powder and allow the acid to run into
the powder. If the _lump_ effervesces _freely_ the specimen is _calcite_
mineral or limestone rock. If the _lump_ does _not effervesce freely_
but the _powder does_, it is _dolomite_ mineral or dolomite rock,
dolomitic limestone. If neither lump nor powder effervesce it is neither
calcite (ordinary limestone) nor dolomite (dolomitic limestone). In the
latter case, it may be gypsum, barite, Shale, weathered chert, clay, or
fire clay, or other rock.
The composition of dolomite is calcium-magnesium carbonate, CaMg(CO₃)₂,
and when pure runs about 54½ per cent calcium carbonate and 45½ per cent
magnesium carbonate. However, dolomite is _not a mechanical mixture_ of
the two carbonates; it is a single crystalline compound wherein the
calcium and magnesium are securely interlocked within the arrangement of
the atoms. For that reason, the extraction of magnesium metal or other
magnesium compounds from dolomite is so difficult and costly that other
magnesium minerals, although not nearly so abundant and accessible to
industry as dolomite, have been processed to obtain the lightweight
metal magnesium.
The thick beds of Missouri dolomitic limestone (and some fairly pure
dolomite) have been used chiefly as agricultural stone for soil
sweetening, for building stone, gravel, and other purposes to which
rough stone is put.