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.

Identifying feldspar in granite.

There are two main types of feldspar. Cases like that are helpful for learning to tell the feldspars apart. Check the color of the rock you suspect is granite. Feldspar biotite gabbro intrusive gabbro is a coarse grained rock that is high is iron magnesium bearing minerals pyroxenes amphiboles plagioclase feldspar olivene.

Generally it has a salt and pepper appearance about black and white. It sometimes also contains hornblende augite magnetite or zircon. The differences can be subtle and confusing. Most of quartz s color comes from feldspar which yields white light gray yellowish or pink tones.

Look at the fracture pattern. Feldspar quartz mica hornblend equivalent to. The polished granite actually a quartz syenite of a park bench displays large grains of the alkali feldspar mineral microcline. Granite is formed by magma that cools very slowly into hard rock below or within the earth s crust.

There is no horizontal banding in. 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. This lighter color is mixed with grains of other darker minerals creating the salt and pepper look. 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.

Applying this definition requires the mineral identification and quantification abilities of a competent geologist. 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. Visible crystals of pink feldspar white or grey quartz and black mica. Granite is made mainly of quartz feldspar biotite and muscovite.

Alkali feldspar also called potassium feldspar or k feldspar has a color range from white to brick red and it s typically opaque. Whereas quartz is an important mineral in the granite it s lacking in syenite. 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. Color is determined by mineral content.