Page 239 - Drilling Technology in Nontechnical Language

230 Drilling Technology in Nontechnical Language Second Edition

Fig. 10–2. Oil on mud returning from the well

Color. Color is the first property that may be noticed in minerals.
Some transparent minerals are shaded different colors by slight impurities
such as iron or titanium. Certain types of quartz are good examples of this.
Luster. Luster is the appearance of light reflected from the surface of

a mineral. Two typical lusters are metallic and nonmetallic. Nonmetallic
lusters have self-descriptive names such as greasy, glassy, silky, and earthy.
Transparency/translucency. A few minerals are transparent in thin
sheets, while others are translucent (they transmit light but not an image).
The majority are opaque (do not transmit light).
Crystals shapes and form. The form that a mineral crystal takes can
also be diagnostic. Some minerals have characteristic crystals, for example
cubes or pyramids, whereas other minerals have no crystal form.
Cleavage. The tendency for some minerals to break along planar
surfaces is called cleavage. Three aspects of mineral cleavage are the
following:
▪ The number of cleavage surfaces of different directions
▪ The quality of the surfaces, e.g., poor, excellent, or pitted

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