What is the difference between plagioclase feldspar and potassium feldspar?

The feldspars are divided into two main groups: Potassium feldspar (“K-spar”) and plagioclase (“plag”). Both display two cleavages and an overlapping range of colors, but only plagioclase displays tiny grooves on one cleavage known as striations. Note the two cleavage surfaces and one fracture surface.

What are the 3 types of feldspar?

All minerals in this grouping have the same crystalline structure. The feldspar group has nearly 20 recognized members, but only nine of those are common….The main feldspars in this grouping include:

Oligoclase.
Andesine.
Labradorite.
Bytownite.
Anorthite.

Is plagioclase an alkali feldspar?

The most common members of the feldspar group are the plagioclase (sodium-calcium) feldspars and the alkali (potassium-sodium) feldspars. Feldspars are also found in many types of sedimentary rocks.

What physical property field test is the definitive way to tell the difference between plagioclase and orthoclase?

Plagioclase is usually white to light gray in color, although color is not a reliable mineral indicator. More definitive in distinguishing plagioclase from orthoclase is the presence of fine parallel lines called “striations” on plagioclase – these striations do not occur with orthoclase.

How do I know if I have feldspar?

Feldspars usually are white or nearly white, though they may be clear or light shades of orange or buff. They usually have a glassy luster. Feldspar is called a rock-forming mineral, very common, and usually makes up a large part of the rock.

Is potassium feldspar the same as orthoclase?

Orthoclase, or orthoclase feldspar (endmember formula KAlSi3O8), is an important tectosilicate mineral which forms igneous rock. The name is from the Ancient Greek for “straight fracture,” because its two cleavage planes are at right angles to each other. It is a type of potassium feldspar, also known as K-feldspar.

What are the Diagnostic properties for feldspar?

Right-angle cleavage: One of the most diagnostic properties of feldspar is its two directions of cleavage that usually intersect at or close to ninety degrees . Properties of Feldspar Minerals Although there are many feldspar minerals, they all share a tight range of physical properties that are surprisingly consistent.

What does plagioclase mean?

Plagioclase is a series of tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more properly known as the plagioclase feldspar series…

What color streak does feldspar make?

In general, potassium feldspars commonly have pink to reddish hues, while the plagioclase feldspars tend to be white or gray, but both mineral groups may exhibit similar colors, so the presence or absence of striations is more diagnostic.

Is feldspar a silicate or a non silicate mineral?

The vast majority of the minerals that make up the rocks of Earth’s crust are silicate minerals. These include minerals such as quartz, feldspar, mica, amphibole, pyroxene, olivine, and a variety of clay minerals.