Alkali Feldspar Granite Thin Section

Many rocks have both feldspars like granite.

Alkali feldspar granite thin section. Biotite metaluminous granite showing a close up of one crystal. The abundance of k spar gives the rock a predominant pink to reddish hue. Orthoclase and sanidine are both optically monoclinic k. At ph 2 o 200 mpa any feldspar precipitated from a melt is a homogeneous alkali feldspar solid solution.

Large number of pages viewed. Earlier workers interpreted the lottah granite as a metasomatised differentiate of the poimena granite. Peppered with minor amounts of black minerals. Microcline is a triclinic k feldspar and has a characteristic cross hatched tartan pattern of twinning seen with a petrographic microscope.

In thin section alkali feldspar grains often look like they re sprinkled with dirt ppl or tiny confetti xpl. It is a dense rock with a phaneritic texture. 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. I have the following thin section of alkali feldspar granite.

Cases like that are helpful for learning to tell the feldspars apart. Alkali feldspar also called potassium feldspar or k feldspar has a color range from white to brick red and it s typically opaque. Are blue minerals arfvedsonite. 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.

This means that biotite in standard thin sections rarely goes completely extinct. 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. Most alkali feldspars are compositionally closer to or end member which explains why we often refer to them as k feldspars potassium feldspars. Microcline is a regular and essential ingredient of sandstone especially feldspar arenaceous rocks and feldspar graywacke sections 5 5 3 2 and 5 5 3 3 section 5 5 3 2 section 5 5 3 3.

Damage produced during thin section grinding causes speckles of light in the biotite where the crystal lattice has been deformed. The differences can be subtle and confusing.