Identifying Feldspar In Granite

Feldspar is often the most abundant rock in a granite this is why the rock looks white with dark spots and not dark with white spots.

Identifying feldspar in granite.

Careful examination will show that syenite is composed of long prisms of the dark mineral hornblende rather than the scaly biotite mica and feldspar which is the chief component of the rock. Cases like that are helpful for learning to tell the feldspars apart. The differences can be subtle and confusing. Today prudent geologists identify potassium feldspars other than sanidine simply as alkali or in some cases potassium feldspars when describing rocks on the basis of macroscopic examination.

Granite is formed by magma that cools very slowly into hard rock below or within the earth s crust. Granite but is distinguished in the hand specimen by the absence of visible quartz. Generally it has a salt and pepper appearance about black and white. Color is determined by mineral content.

There is no horizontal banding in. There are two main types of feldspar. This lighter color is mixed with grains of other darker minerals creating the salt and pepper look. Alkali feldspar also called potassium feldspar or k feldspar has a color range from white to brick red and it s typically opaque.

Applying this definition requires the mineral identification and quantification abilities of a competent geologist. Visible crystals of pink feldspar white or grey quartz and black mica. More below alkali feldspar has the general formula k na alsi 3 o 8 but varies in crystal structure depending on the temperature it crystallized at. Most of quartz s color comes from feldspar which yields white light gray yellowish or pink tones.

Granite is a plutonic rock in which quartz makes up between 10 and 50 percent of the felsic components and alkali feldspar accounts for 65 to 90 percent of the total feldspar content. Look at the fracture pattern. Feldspar quartz mica hornblend equivalent to. Many rocks have both feldspars like granite.

Granite always consists of quartz and feldspar which usually give granite a light almost glittery color ranging from almost translucent white from the quartz to a pale pink from the feldspar. It sometimes also contains hornblende augite magnetite or zircon. Whereas quartz is an important mineral in the granite it s lacking in syenite. The polished granite actually a quartz syenite of a park bench displays large grains of the alkali feldspar mineral microcline.