Schist is a medium-grade metamorphic rock with medium to large, flat, sheet-like grains in a preferred orientation (nearby grains are roughly parallel). It is defined by having more than 50% platy and elongated minerals, often finely interleaved with quartz andfeldspar. These lamellar (flat, planar)minerals include micas, chlorite, talc, hornblende, graphite, and others.
Quartz often occurs in drawn-out grains to such an extent that a particular form called quartz schist is produced. Schist is often garnetiferous. Schist forms at a higher temperature and has large grains (metamorphic arrangement in layers) with medium to large grained flakes in a preferred sheet like orientation is called schistosity.
The names of various schist’s are derived from their mineral constituents. Schist’s rich in mica are called mica schist’s, and include biotite or muscovite.
The individual mineral grains in schist, drawn out into flaky scales by heat and pressure, can be seen by the naked eye. Schist is characteristically foliated, meaning the individual mineral grains split off easily into flakes or slabs.
Most schist’s have been derived from clays and muds which have passed through a series of metamorphic processes involving the production of shale´s, slates and phyllites as intermediate steps. Certain schist’s have been derived from fine-grained igneous rocks such as basalts and tuffs. Most schist’s are mica schist’s, but graphite and chlorite schist’s are also common.
Schist’s are named for their prominent or perhaps unusual mineral constituents, such as garnet schist, tourmaline schist, glaucophane schist, etc.
The schist’s are classified principally according to the minerals they consist of and on their chemical composition. For example, many metamorphic limestone’s, marbles, and calc-schists, with crystalline dolomites, contain silicate minerals such as mica, tremolite, diopside, scapolite, quartz and feldspar. They are derived from calcareous sediments of different degrees of purity. Another group is rich in quartz (quartzites, quartz schist’s and quartzose gneisses), with variable amounts of white and black mica, garnet, feldspar, zoisite and hornblende. These were once sandstones and erinaceous rocks. The graphitic schist’s may readily be believed to represent sediments once containing coal or plant remains; there are also schistose ironstones (hematite-schist’s), but metamorphic beds of salt or gypsum are exceedingly uncommon. Among schist’s of igneous origin there are the silky calc-schists, the foliated serpentines (once últarmafic masses rich in olivine), and the white mica-schist’s, porphyries and banded halleflintas, which have been derived from rhyolites, quartz-porphyries and felsic tuffs. The majority of mica-schist’s, however, are altered clay stones and shale’s, and pass into the normal sedimentary rocks through various types of phyolite and mica-slates. They are among the most common metamorphic rocks; some of them are graphitic and others calcareous. The diversity in appearance and composition is very great, but they form a well-defined group not difficult to recognize, from the abundance of black and white micas and their thin, foliated, schistose character. A subgroup is the andalusite, staurolite, kyanite and sillimanite-schists which usually make their appearance in the vicinity of gneissose granites, and have presumably been affected by contact metamorphism.
At this location.
Where you are standing the chist was made 200 Million years ago, it was formed under intense heat and pressure, igneous rock and quartz became molten, trapping gold, tungsten, lead, cupper, iron and sulphur in fractures and faults which some can easily be seen in the schist at this location.
The glaciation formed the landscape we see today from 1.000.000 to 10.000 years ago, as the glacier forged it way forward down the many valleys the glaciers carried and crushed tons of quartz, torn away from the reefs the gold bearing quarts was widely scattered which evidently made the gold rush around Arrow town and other places in the region.
To clame this cache you will have to answer the following questions and email them to us before logging the cache, if there is something wrong with your answers we will contact you.
At GZ there are a number of schist’s blocks, if you are facing the lake and look at the block mostly to the right describe the colors of this block.
What minerals and deposits do you see in this block.
Are the quartz in this block millimeters or centimeters thick
Optional, please take a picture óf your gps and your team and post it together with your log
All armchair loggings will be deleted.