How do you identify a mineral in the thin section?

We use cross-polarized light to learn a crystal’s optic class and optic sign, to measure extinction angles and sign of elongation, and to measure 2V. A combination of optical properties allows us to identify minerals in thin section and to interpret geologic histories.

How do you identify quartz in a thin section?

In thin section, when viewed in plane polarized light (PPL), quartz is colorless with low relief and no cleavage. Its habit is either fairly equant or anhedral if it infills around other minerals as a cement.

How can you identify a tourmaline in a thin section?

Tourmaline thin section

  1. Formula: (Na,Ca)(Mg,Li,Al,Fe2+)3Al6 (BO3)3Si6O18(OH)4
  2. System: Trigonal.
  3. Color: Pale brown to dark-brown to brownish-black, also dark-yellow, blue.
  4. Lustre: Vitreous, Resinous.
  5. Hardness: 7.
  6. Density: 2.9–3.1.

How do you identify calcite in the thin section?

Distinguishing Features Thin section: high order colors under crossed polars, very high relief that changes with rotation, lower refractive index than dolomite, simple twinning and lamellar twins on some crystal faces, rhobohedral cleavage.

Why do geologists use thin sections of rocks?

Thin sections are prepared in order to investigate the optical properties of the minerals in the rock. This work is a part of petrology and helps to reveal the origin and evolution of the parent rock.

How can you tell if you have tourmaline?

If you have a tourmaline crystal, identification should be easy.

  1. Tourmaline has a prismatic crystal habit and often has obvious striations that parallel the long axis of a crystal.
  2. Tourmaline crystals often have triangular or six-sided cross-sections with rounded edges.

How can you identify an olivine in a thin section?

Olivine Optical Properties Colorless to pale green in thin section. Weak, pale green pleochroism in thin section. Olivine is commonly recognized by it high retardation, distinctive fracturing, lack of cleavage, and alteration to serpentine. Colorless to olive green in thin section.