Contents
- 1 How can you distinguish muscovite from biotite in thin section?
- 2 What is the luster of biotite?
- 3 How can you tell Hornitende and Augite apart?
- 4 How can you identify an olivine in a thin section?
- 5 How can you tell biotite?
- 6 Is biotite magnetic?
- 7 How do you identify an epidote in a thin section?
- 8 What does biotite look like with low Fe content?
- 9 What kind of color is a biotite flake?
- 10 What are the physical properties of biotite mineral?
How can you distinguish muscovite from biotite in thin section?
The mica minerals have one perfect cleavage that allows them to be broken into very thin sheets. This is very distinctive. Muscovite is clear, silvery, or coppery silver in color (depending on the thickness of the sample and presence of impurities) whereas fresh biotite is black.
What is the luster of biotite?
It can be transparent to opaque, has a vitreous to pearly luster, and a grey-white streak. When biotite crystals are found in large chunks, they are called “books” because they resemble books with pages of many sheets.
Does biotite have a streak?
Biotite is a rock-forming mineral found in a wide range of crystalline igneous rocks such as granite, diorite, gabbro, peridotite, and pegmatite….
| Physical Properties of Biotite | |
|---|---|
| Chemical Classification | Dark mica |
| Color | Black, dark green, dark brown |
| Streak | White to gray, flakes often produced |
| Luster | Vitreous |
How can you tell Hornitende and Augite apart?
Augite (a pyroxene) Augite is most easily confused with hornblende. Hornblende has highly reflective cleavages whereas augite cleavages are dull. Hornblende tends to form elongate rectangular crystals whereas augite crystals tend to be blocky.
How can you identify an olivine in a 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.
How can you identify a sillimanite in a thin section?
Distinguishing Features High relief, moderate birefringence, parallel extiction, and slender prismatic or fibrous crystal habit. Distinctive diamond-shaped cross sections with cleavage for prismatic grains. Fibrous mats commonly replace biotite.
How can you tell biotite?
In general, keys to identifying biotite are its color and pleochrism, cleavage, optical texture and characteristic extinction, and habit. Biotite’s features generally make identification unambiguous. However, in some medium-grade metamorphic rocks and volcanic rocks, the features are less prominent.
Is biotite magnetic?
The platy morphology of biotite facilitates magnetic measurements with the applied field either in the plane of the sheets (Xe⊥ ) or perpendicular to the plane (Xe∥). Thus, biotite has both magnetic and structural two‐dimensional aspects.
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.
How do you identify an epidote in a thin section?
Distinguishing Features Epidote is characterized by its green color and one perfect cleavage. H= 6-7. G = 3.25 to 4.45. Streak is white to gray.
What does biotite look like with low Fe content?
For biotite with low Fe-content (phlogopite), coloration is more subtle (clear, light browns and tans). · Habit and cleavage – often appears as tabs or long skinny flakes which may be bent. It shows one excellent cleavage, depending on grain orientation.
How can you tell the difference between biotite and hornblende?
You notice that he already knew that he had biotite and hornblende. He wanted a better clue as to their ID in a thin section not a hand specimen. Optical propeeties are a much more definitive way to determine chemical structure of the minerals thn hand specimens.
What kind of color is a biotite flake?
In this view, one large flake of biotite dominates the top half of the photos. It is light brown (PP). In XP light it shows a pebbly texture and mostly second order green interference color (XP). Most of the clear mineral matter beneath the biotite is anthophyllite, an amphibole.
What are the physical properties of biotite mineral?
Physical Properties of Biotite Chemical Classification Dark mica Color Black, dark green, dark brown Streak White to gray, flakes often produced Luster Vitreous Diaphaneity Thin sheets are transparent to transluce