To further comprehend the difference between plagioclase and feldspars, you must first realize that plagioclase is a kind of feldspar. In general, feldspars are quartz-like rocks and plagioclases are mafic rocks. Both have similar chemical makeup and physical structure. However, they have different roles in the environment. Plagioclase is the dominant mineral in igneous rocks while feldspars are more common in metamorphic rocks. In order to understand these differences, let’s look at the chemistry of feldspars and plagioclases. FeO + SiO2 2(FeSi)O For both feldspars (quartz) and plagioclases (mica), you begin with either silicon dioxide or iron oxide. When these two elements combine, you get just two silicates - ferrous silicate and aluminum silicate. These are called the basic building blocks of feldspars (or quartz).
- Feldspathorien is the name given to a group of minerals that have similar chemical compositions. There are three groups of feldspathorien: plagioclases, orthoclases, and albite.
Plagioclases are generally white and transparent; they tend to be brittle, whereas orthoclases are more yellowish and softer. Albite is grayish-white, hard, and brittle. These minerals appear as mica schists, gneisses, granites, and igneous rocks. Feldspathories are the best-known example of feldspar-group minerals. Feldspathoriet is the name given to feldspar minerals. Feldspatholite is the name given to zeolites, faujasite, phlogopite, etc. , which are minerals composed mainly of silicates and alumina.
- Plagioclase forms both single crystals and aggregates. In the case of aggregates, the grains are cemented together by glassy material called authigen.
When formed as single crystals, these minerals may be elongated rods, flat plates, or needles. Plagioclases commonly occur in granite, gabbro, and basalts. Orthoclases are less common than plagioclases. They are almost always dark-colored and are often referred to as metamorphosed plagioclases. Orthoclases may be either monoclinic or triclinic.
- Most feldspathoids are crystalline solids with specific crystal structures. The most common feldspatholite structure is the cage structure.
Other feldspathorium structures include chainlike (chain structure), sheetlike (sheet structure), rodlike (rod structure), spindle (needle structure), platelet (plate structure), and tabular (tabular structure), tectonic (tectonic structure), and vesicular (vesicle structure).
- Feldspar occurs in two basic types: primary and secondary. Primary feldspar is chemically purer than secondary feldspar. Secondary feldspar contains quartz and/or kaolin impurities.
Primary feldspar includes quartz, microcline, muscovite, biotite, K-feldspar, cordierite, etc. Secondary feldspar contains quartz, pyroxene, albite, amphibole, chalcedony, apatite, hematite, goethite, illite, kaolin, kyanite, lepidolite, montmorillonite, pyrite, pyrophillite, serpentine, smectite, talc, tourmaline, zircon, zoisite, etc. There are over 200 different species of primary feldspar and 50+ species of secondary feldspar! Plagioclase feldspar is commonly found as igneous rocks in granite and basalt which are very hard and strong stones. The plagioclase feldspars can be generally classified into two types: plagioclase, and orthoclase feldspars. They differ only slightly in chemical composition. One main difference between them is the amount of iron present. Orthoclase feldspar has more than plagioclase. They are different minerals but similar in appearance. Both have a silica base and an alumina end member. The name “plagioclase” comes from the Greek words meaning “having many faces” or “polyhedron” referring to the way it looks when viewed under a microscope. 
- Plagioclase (pronounced PLAG-ee-o-CLAYZ) is a mineral composed primarily of silica. It is often mistaken for feldspar because both minerals have similar physical characteristics. However, they are actually different minerals.
Plagioclase crystals consist of 2 or more layers of silicon dioxide while feldspar consists only of a single layer. Plagioclase is what geologists call igneous rocks, meaning they are formed from magma rather than lava. Unlike feldspar, they do not weather away over time.
- When a volcanic eruption occurs, the ground below erupts giving off immense amounts of heat, ash, gases, and magma.
As the surface cools, the magma crystallizes leaving behind solidified lava and magma. As magma cools, it turns into granite or basalt. These are considered sedimentary rocks and are mostly composed of quartz, feldspar, mafic minerals, and sometimes small amounts of muscovite. Feldspar minerals are white/light gray due to their high concentration of magnesium and aluminum. Feldspathic plagioclases are the most abundant igneous minerals. 
The term "plagioclase" means layered or laminated. Most feldspars are formed as large crystals which have been folded into layers. Feldspathic plagioclase is commonly called "feldspars" since they were first described as "field spars". Feldspar is the common name of these rocks. Felspathic plagioclases occur primarily as small single crystals or tabular grains. They occur almost everywhere and there are volcanic eruptions. They can be found in pegmatites as well as in granitoid. Feldspar is an important rock because it contains silicon dioxide (SiO2), aluminum oxide (Al2O3), magnesium oxide (MgO), iron oxides (e.g., goethite FeO₃·OH and lepidocrocite FeO₄·(H2O)), and potassium feldspar (KAlSi3O8). Plagioclase feldspars are a group of minerals that have similar chemical compositions but differ in their crystal structure. They are commonly found as monoclinic crystals in igneous rocks and granitic pegmatites. In contrast to plagioclase which has a rhombohedral crystal form, albite is usually triclinic. Biotite is an important member of the feldspar family. Feldspars can be used as building blocks in ceramics or as a fluxing agent in metallurgy. 
Most feldspars are translucent and colorless. Feldspars provide hardness due to their high silica content. Feldspar is a hard mineral. It is a common constituent of granite and is often present as a crystalline rock within kimberlite pipes, indicating its importance as a source rock for diamond mining. Feldspars make up 10% of most crustal rocks. Some are considered more valuable than others. For example, plagioclase feldspar contains about 7% magnesium oxide whereas biotite feldspar has 3%. Magnesium oxide can be extracted economically from both types of feldspar. Plagioclases are the second most abundant mineral group after phyllosilicates. Feldspars are silicate minerals that have high aluminum content. Plagioclase refers to a class of feldspar; they are chemically composed of the elements Al2SiO5. These substances are highly refractory and less soluble than silica, making them the third most abundant mineral group after quartz and feldspars. 
Feldspars are a group of igneous rocks composed primarily of aluminous silicate minerals. They have been formed by partial melting of granitic magma intruded into sedimentary rocks, resulting in the formation of two types of feldspar: monomineralic feldspars (e.g., biotite) and polymineralic feldspar (e.g., wollastonite). Both are found in granite and represent about 10% of the total volume of the rock. The Plagioclase Group represents more than 85% of igneous rocks and includes the following minerals: augite, diopside, leucite, hornblende, microcline, olivine, pyroxene, sanidine, talcite, troctolit, tourmaline, ulvöspinel, yttrium-stabilized zircon. Feldspar group consists of the following minerals: analcime, bassanite, chalcedony, chromite, cordierite, euclase, garnet, gres, hematite, ilmenite, kyanite, molybdenite, montmorillonite, nepheline syenite, orthopyroxene, phengite, rutile, sillimanite, staurolite, titanite, topaz, tschermakite, xenotime. 
Quartz is the hardest mineral on earth known to man. It has many uses including glass production; however, it is not commonly used in the world today for construction and landscaping purposes due to its low quality. Quartz is mined for use in jewelry, abrasives, and ceramics. Silica is the most abundant mineral on Earth and accounts for more than 90% of Earth's crust. It is derived from volcanic eruptions and is the major constituent of sand and gravel. It is found in many forms: silicon dioxide, silicates, and silicic acid. Silicon dioxide occurs naturally as quartz, tridymite, cristobalite, and fayalite. Feldspars contain relatively low amounts of impurities compared to other minerals. Feldspars are composed of alumina, silica, iron oxide, and occasionally titanium oxide. Feldspars may occur in three different crystalline structures: microcrystalline, intermediate, and macro fibrous. Microcrystals typically show no trace of any other impurity. The intermediate structure contains up to 20% of accessory minerals. Microfiber feldspars consist of long fibrous crystals that contain impurities.