Identifying Feldspar In Granite

There is no horizontal banding in.

Identifying feldspar in granite.

There are two main types of feldspar. This lighter color is mixed with grains of other darker minerals creating the salt and pepper look. 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.

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. Many rocks have both feldspars like granite. The differences can be subtle and confusing. 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.

Look at the fracture pattern. Visible crystals of pink feldspar white or grey quartz and black mica. Check the color of the rock you suspect is granite. 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.

Feldspar quartz mica hornblend equivalent to. Most of quartz s color comes from feldspar which yields white light gray yellowish or pink tones. The polished granite actually a quartz syenite of a park bench displays large grains of the alkali feldspar mineral microcline. Generally it has a salt and pepper appearance about black and white.

Color is determined by mineral content. Granite but is distinguished in the hand specimen by the absence of visible quartz. Granite is made mainly of quartz feldspar biotite and muscovite. 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.

Granite is formed by magma that cools very slowly into hard rock below or within the earth s crust. Feldspar biotite gabbro intrusive gabbro is a coarse grained rock that is high is iron magnesium bearing minerals pyroxenes amphiboles plagioclase feldspar olivene. 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. 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.