Identifying Feldspar In Granite

Feldspar quartz mica hornblend equivalent to.

Identifying feldspar in granite.

Granite is formed by magma that cools very slowly into hard rock below or within the earth s crust. 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. Most of quartz s color comes from feldspar which yields white light gray yellowish or pink tones. Cases like that are helpful for learning to tell the feldspars apart.

Feldspar biotite gabbro intrusive gabbro is a coarse grained rock that is high is iron magnesium bearing minerals pyroxenes amphiboles plagioclase feldspar olivene. The polished granite actually a quartz syenite of a park bench displays large grains of the alkali feldspar mineral microcline. Applying this definition requires the mineral identification and quantification abilities of a competent geologist. This lighter color is mixed with grains of other darker minerals creating the salt and pepper look.

Look at the fracture pattern. 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. Check the color of the rock you suspect is 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.

Color is determined by mineral content. Alkali feldspar also called potassium feldspar or k feldspar has a color range from white to brick red and it s typically opaque. There are two main types of feldspar. 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 but is distinguished in the hand specimen by the absence of visible quartz. Many rocks have both feldspars like granite. Whereas quartz is an important mineral in the granite it s lacking in syenite. It sometimes also contains hornblende augite magnetite or zircon.

Granite is made mainly of quartz feldspar biotite and muscovite. 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. The differences can be subtle and confusing. Generally it has a salt and pepper appearance about black and white.