Feldspar Classification and Feldspar Grinding Mill


About Feldspar

Feldspar is the generic name for Feldspar-group minerals. It is a common aluminosilicate rock forming minerals containing calcium, sodium, and potassium. Feldspar is found in the Earth's crust at up to 60% of its mass, and can occur in igneous, metamorphic, and sedimentary rocks. Feldspar is a major mineral component of nearly all igneous rocks and is important for rock classification.


Feldspar Classfication

In general, feldspar is divided into two categories —— orthoclase (potassium feldspar) and plagioclase(soda feldspar). The difference between the two is in the angle between the two sets of clefts, with the orthoclase equal to 90 degrees and the plagioclase less than 90 degrees. The common card twin, thin section identification property of orthoclase is that the extinction of the twin consists of two parts, black and white, under an orthorhombic polarizing mirror, which is also one of the differences between plagioclase, which is typically a laminated twin, and orthoclase, which is under a mirror.



The Difference of Orthoclase and Plagioclase

  1. Different Physical Characteristics
Orthoclase : The transparent orthoclase exhibits similarities to topaz, beryl, light yellow topaz, and glass. Varieties such as long-chain orthoclase, starlight orthoclase, orthoclase solar rock, and orthoclase lunar rock have been discovered. Consequently, the significance of orthoclase gems cannot be overstated. Its refractive index ranges from 1.520 to 1.525 with a birefringence of 0.005 and specific gravity ranging from 2.56 to 2.59 alongside a hardness rating of 6.
Plagioclase : The occurrence of dense polycrystalline twins, which are white and gray in color and possess a hardness greater than that of a knife, is commonly observed within crystals or along cleavage planes. These twins frequently coexist with common pyroxene and olivine minerals in dark rocks such as gabbro and peridotite.
  1. Differing in Nature
Orthoclase : In the monoclinic crystal system, crystals are typically short columnar or thick plate-shaped, with common twinning and also granular or blocky aggregates.
Plagioclase : A complete isomorphic series of Ab-An minerals exists in the feldspar group, but they are miscible with each other within certain temperature ranges at room temperature, resulting in a microscopic association of two-phase feldspar.
  1. Different Melting Point
The melting point of potassium feldspar is 1290℃, whereas that of albite is 1215℃. Natural feldspar commonly exists as a solid solution, resulting in a lower melting point than single-composition feldspar. Feldspar exhibits excellent process properties with a wide melting interval and optimal performance between temperatures of 1200 °C and 1350 °C when it becomes transparent and highly viscous. In contrast, albite has a narrow melt interval and low viscosity, making it susceptible to deformation during sintering.
Furthermore, feldspar functions effectively as a fluxing agent; for instance, if added to the Al2O3-SiO2 system, the liquid phase appears at approximately 985°C ±20°C with an initial melting temperature that decreases as the content of feldspar increases. At equivalent temperatures, albite exerts greater fluxing effects than potassium feldspar.


The Applications of Feldspar

Feldspar constitutes a significant portion of the raw materials utilized in the production of ceramics and glass.

Glass Industry
Feldspar is a crucial constituent of glass mixtures, with potassium feldspar accounting for approximately 50% to 60% of the total in the glass industry. Its primary functions are as follows:
  1. Potassium feldspar, abundant in Al2O3 and low in iron content, supplies the necessary Al2O3 for glass ingredients, thereby reducing the melting temperature of glass and minimizing the usage of soda ash. This enhances the toughness, strength, and resistance to acid and alkali erosion of glass.
  1. The transformation process from potassium feldspar to molten glass occurs relatively slowly with limited crystallization capacity. This prevents crystal precipitation during glass formation that could disrupt normal production or lead to defects.
  1. It can adjust the viscosity of glass to enhance its processing adaptability.
Ceramic Glaze
The ceramic glaze is primarily composed of raw materials such as feldspar, quartz, and clay. Potassium feldspar, which is the most commonly used component, can account for 10% to 35% of the total amount. It plays a crucial role in forming the glass phase due to its wide melting range and high temperature viscosity. This expands the maturation temperature range of the glaze and facilitates reducing firing temperature while enhancing glossiness, transparency, and smoothness of the glaze layer. Moreover, it improves chemical stability and elevates product grade and quality level.

Feldspar Grinding Mill

HGM Ultrafine Grinding Mill
Capacity: 0.2-45 t/h
Feed Size: ≤20 mm
Powder Fineness: 325-3000 mesh

The ultrafine grinding mill boasts high efficiency and low consumption. With the same fineness of finished product and motor power, its output is twice that of air mills, stirring mills, and ball mills while consuming only 30% as much energy. Furthermore, the wear-resistant materials used for the grinding roller and ring extend their service life two to three times longer. This mill features a rigorous design with no screws or bearings in the grinding chamber to prevent damage caused by screw loosening. Additionally, it can achieve a high powder fineness (325-3000 mesh) that can be adjusted at any time.