Limestone Exploration: Identify Calcite, Dolomite, and Clay

Limestone is used in a variety of commercial and industrial products, from Portland cement to aggregate (gravel) to powdered limestone for steel processing, to decorative marble. During exploration geologists often must identify the minerals typically found in limestone, including calcite, dolomite, quartz, pyrite, and clay. Calcite and dolomite are the key ingredients in commercially valuable limestone deposits and it is often difficult to distinguish these minerals from clays in the mixture.

Classification of limestone:

  • Calcite limestone – more than 90% calcite and 10 % dolomite
  • Dolomitic Limestone – calcite 50-90% with dolomite 10-50%
  • Calcite dolomite – calcite 10-50% and dolomite 50-90%
  • Dolomite – calcite less than 10% with dolomite more than 90%

With the oreXpress field spectrometer, scans of prospective limestone deposits can be taken in the field and identified for the different minerals using EZ-ID mineral identification software.

The oreXpress is lightweight, rugged and reliable. Throw it in a backpack with its lithium-ion batteries and you have around 4 hours of scanning from each battery. With all solid state photodiode array design, there are no moving optical parts for breakage or misalignment.

With its high resolution and great sensitivity, the oreXpress delivers clear and accurate scans that EZ-ID can identify by marching to three libraries of 2600 spectra for 1100 minerals. Each mineral has a distinctive spectra. In our limestone sample, kaolinite clay is differentiated by the doublet absorption features near 1400nm and 2200nm. Calcite and dolomite share similar features but can be separately identified. Dolomite has prominent features at 1858, 1978, and 2320nm. Calcite has features at 1875, 1995, and 2330nm.

Dolomite identified by EZ-ID mineral identification software.

Calcite identified by EZ-ID mineral identification software.

Kaolinitie identified by EZ-ID mineral identification software. Note the two doublets.