How can you identify an amphibole in a thin section?

How can you identify an amphibole in a thin section?

In thin sections, amphiboles are distinguished by several properties, including two directions of cleavage at approximately 56° and 124°, six-sided basal cross sections, characteristic colour, and pleochroism (colour variance with the direction of light propagation).

How do you identify hornblende in a thin section?

In PPL a thin section of Hornblende ranges from yellow -green to dark brown. Green varieties usually have X= light yellow green, Y=green or grey-green and Z=dark green. Brownish varieties have X=greenish-yelow/brown, Y=yellowish to reddish brown and Z=grey to dark brown.

Is amphibole a pleochroic?

Transparent colorless to green, brown, red, yellow, depending on mineralogy within the amphibole group. Strongly pleochroic. Moderate birefringence may be masked by color.

Is hornblende a pleochroic?

Hornblende is generally pleochroic, often in shades of green, blue, brown, and less commonly red or yellow. This example is in shades of green only, but brown hues are generally more common.

How do you identify minerals in a 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.

What is Pleochroic scheme?

Pleochroism Table. Light passing through some crystals is absorbed differently in different directions. Commonly, different wavelengths of light (colors of light) are absorbed different amounts in different directions. The color we see is the color of light after the absorbed wavelengths have been removed.

Is Clinopyroxene a Pleochroic?

Clinopyroxene – XYZ2O. Optical properties: Colour and Pleochroism: Usually colourless, gray, pale green or pale brown, darker colours associated with Fe-rich varieties titanaugite is more distinctly coloured from brown/pink to violet. Cleavage: Parallel to {110}, which intersect at 90°.

Is Clinopyroxene a pleochroic?

Which crystal system is non pleochroic?

Gemstones such as diamonds and garnets belong to the isometric or cubic crystal system. These gems have a single RI, so no matter the viewing angle, they only show one color. They’re non-pleochroic.

What is the characteristic of amphibole?

Typically, amphiboles form as long prismatic crystals, radiating sprays and fibrous aggregates. They are generally dark coloured though their colours can range from colourless to white, green, brown, black, blue or lavender. This property is related to composition, particularly iron content.

What is PPL and XPL in geology?

PPL=plane polarized light; XPL = cross polarized light.

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.

Which mineral is non-pleochroic?

Pleochroism = “many colored”