Page 240 - Drilling Technology in Nontechnical Language

Chapter 10 – EVALUATION 231

▪ The angle between the surfaces
Hardness. The hardness of a mineral is quantified by Mohs scale,

which ranges from 1 to 10. A mineral that is higher on the scale can
scratch a mineral that is lower on the scale. The Mohs scale is in order of
increasing hardness:

1. Talc
2. Gypsum
3. Calcite
4. Fluorite

5. Apatite
6. Orthoclase
7. Quartz
8. Topaz

9. Corundum
10. Diamond
Saltiness. Tasting can sometimes identify a mineral. (Not recom-
mended with oil-based mud!)
Acid test. A very important test is the application of cold dilute
hydrochloric acid to a sample. Calcite and the sedimentary rock limestone
made up of predominantly calcite (CaCO ) grains are the only ones that
3
will bubble with dilute acid. Dolomite bubbles slightly, and increased
bubbling will be noted if heat is applied.
Swelling properties. Reaction of clays (hydration) to water or
dilute acid.
Sorting. Distribution and estimation of grain size.
Roundness. Describes a variety of shapes from very angular to well
rounded.
Sphericity. Describes shape from very elongated to very spherical;
high sphericity is spherical, and low sphericity is elongated.
Cementation. The degree of cementation and the mineral type. May
be well cemented, good cementation, or poor cementation.

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