How do you identify chlorite under thin section?
How do you identify chlorite under thin section?
Chlorite thin section
- Formula: (Mg,Fe)3(Si,Al)4O10(OH)2 • (Mg,Fe)3(OH)6
- System: Monoclinic.
- Color: Green, yellowish green, olive green, blackish green, bluish green, white, pink.
- Lustre: Greasy, Pearly, Dull.
- Hardness: 2–2½
- Density: 2.6–3.3.
How do you identify schist in thin section?
In thin section, schist is identified by its coarse texture (coarser than Phyllite) with light and dark bands of minerals. Light coloured minerals being the felsic minerals and darker minerals are of mafic minerals.
What minerals are found in schist?
Most schists are composed largely of platy minerals such as muscovite, chlorite, talc, sericite, biotite, and graphite; feldspar and quartz are much less abundant in schist than in gneiss.
What is the hardness of schist?
What is the hardness of schist? From 4 to 5 on the Moh’s scale, which is only indicative of its relative hardness against other rocks and minerals.
How do you identify a feldspar in a thin section?
In general, keys to identifying K-feldspar are its (lack of) color, its low birefringence, and its twinning. In thin section, microcline, orthoclase and sanidine are distinguished by their twinning, optical sign, and 2Vo.
Where is schist found on Earth?
Before the 18th century, schist, shale, and slate were used interchangeably to describe the same rock. There are various features that distinguish schist rocks made from sedimentary rocks or those made from igneous. It can be found in many countries including Brazil, parts of the US and Ireland.
Which is the dominant mineral in a schist?
Garnet graphite schist is a schist that contains graphite as its dominant mineral, but abundant garnet is visible and present. Garnet mica schist in thin section: This is a microscopic view of a garnet grain that has grown in schist. The large black grain is the garnet, the red elongate grains are mica flakes.
What causes chlorite schist to lose its schistosity?
This force may be compressive (in mountain ranges) or simply caused by the weight of the overlying rocks. Metamorphic reactions between minerals upon increased burial will lead to the loss of schistosity because feldspar increases in abundance as micas become unstable.
What do the feldspars alter to in chlorite?
The feldspars alter to sericite, which is a catch-all name for fine-grained white mica whose identity can’t be pinned down just by looking at a thin section. This chlorite grain is surrounded by sericitized feldspars.
How does a metamorphic rock become a schist?
This metamorphic environment is intense enough to convert the clay minerals of the sedimentary rocks into platy metamorphic minerals such as muscovite, biotite, and chlorite. To become schist, a shale must be metamorphosed in steps through slate and then through phyllite.