As the magma evolves toward more fe rich compositions the chromite also becomes more fe rich and less transparent.
Tourmaline granite thin section.
Minerals in thin section 2000 perkins dexter and henke kevin.
Some relict skeletal feldspar.
It also exhibits intense pleochroism.
Every shipment will have a different structure and supply is limited.
Longitudinal sections are usually roughly rectangular.
In this mode of occurrence tourmaline rarely makes up more than a few percent of the rock s volume.
Cross polarized light photomicrograph of tourmaline in sample cv 114 from the strathbogie granite australia.
This is a thin section of tourmaline granite from cornwall.
The thin section has been slightly rotated to show the characteristic change in color of the tourmaline known as pleochroism.
Also found in metasomatically altered limestone and dolomite in contact metamorphic zones.
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In granites tourmaline is usually schorl type and it may form by late stage alteration of granitic minerals by pneumatolitic fluid containing boron and extreme tourmalinization may yield a rock of only tourmaline and quarz like luxullianite from the village of luxulyan in cornwall england.
This is a hydrothermally altered granite with brightly coloured xpl tourmaline some skeletal in quartz feldspar.
The calcium phosphate mineral apatite is a common accessory minerals of s type granites.
Tourmaline is also a common mineral in schist gneiss quartzite and phyllite.
Small 250x250 max medium 500x500 max.
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Tourmaline as an accessory mineral the most common occurrence of tourmaline is as an accessory mineral in igneous and metamorphic rocks.
Cr mg al rich chromites are realtively transparent and can be dark brown at full thin section thickness.
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Tourmaline thin section view description.
It is an accessory mineral in granite granodiorite and related felsic rocks.
Tourmaline forms triangular prismatic crystals and can show a range of body colours.
Tourmaline commonly forms euhedral stubby columnar to acicular crystals that show a rounded triangular or crudely hexagonal cross section.
It often occurs as millimeter size crystals scattered through granite pegmatite or gneiss.
Also found as anhedral grains or irregular masses.
Fe rich chromite is typically opaque at full thin section thickness but is transparent dark brown along thin edges.
Acicular crystals may form radiating masses.
