Alkali Feldspar Granite Thin Section

This means that biotite in standard thin sections rarely goes completely extinct.

Alkali feldspar granite thin section.

Orthoclase and sanidine are both optically monoclinic k. The lottah granite is a composite pluton of tin mineralised strongly peraluminous alkali feldspar granite which intrudes the poimena granite a major component of the mid devonian blue tier batholith of northeastern tasmania. Microcline is a triclinic k feldspar and has a characteristic cross hatched tartan pattern of twinning seen with a petrographic microscope. Large number of pages viewed.

Many rocks have both feldspars like granite. Anorthoclase na k alsi 3 o 8 is a crystalline solid solution in the alkali feldspar series in which the sodium aluminum silicate member exists in larger. Earlier workers interpreted the lottah granite as a metasomatised differentiate of the poimena granite. Biotite metaluminous granite showing a close up of one crystal.

Peppered with minor amounts of black minerals. The differences can be subtle and confusing. Are blue minerals arfvedsonite. Most alkali feldspars are compositionally closer to or end member which explains why we often refer to them as k feldspars potassium feldspars.

You can find the explanation on the alkali feldspar page. At ph 2 o 200 mpa any feldspar precipitated from a melt is a homogeneous alkali feldspar solid solution. Alkali feldspar granite some varieties of which are called red granite is a felsic igneous rock and a type of granite rich in the mineral potassium feldspar k spar. Orthoclase is frequently known as potassium feldspar or k spar and is easily distinguished from the plagioclase feldspars in hand sample by its lack of striations.

In thin section alkali feldspar grains often look like they re sprinkled with dirt ppl or tiny confetti xpl. Alkali feldspar also called potassium feldspar or k feldspar has a color range from white to brick red and it s typically opaque. The abundance of k spar gives the rock a predominant pink to reddish hue. It is a dense rock with a phaneritic texture.

Cases like that are helpful for learning to tell the feldspars apart. Damage produced during thin section grinding causes speckles of light in the biotite where the crystal lattice has been deformed.