The chemical formula of Monticellite is indicated by Ca(Mg,Fe)SiO4. Monticellite is a Silicate mineral. It is known to crystallize in the orthorhombic system. In optical mineralogy, the orthorhombic crystal system comprises crystals having three mutually perpendicular axes, of which all are of different lengths. When evaluated under polarizing microscope, Monticellite is known to have biaxial negative figure. The indices of the mineral range from 1.638 to 1.674. The birefringence also ranges from 0.012 to 0.020. The optic angle of Monticellite is usually found at about 69 degree to 88 degree. When evaluated closely under polarized microscope, Monticellite is commonly found having moderately high positive relief.
The hardness measure of the mineral when it is evaluated using the Mohs scale method is usually 5.5. The specific gravity measure of Monticellite is commonly found ranging from 3.05 grams per cubic centimeters to 3.27 grams per cubic centimeters. When evaluated in hand sample, Monticellite is usually found colorless to gray. When rubbed on a white porcelain streak plate, Monticellite is commonly found leaving a white streak. Monticellite is also most commonly found exhibiting a vitreous luster in reflected light of petrographic polarizing microscope.
Monticellite is most commonly found as anhedral, equant or irregular grains. It is usually found colorless in thin section and grain mount. The crystals of this mineral are usually elongate and commonly yield equant to elongate polygonal cross sections with eight or more faces. Monticellite has single poor cleavage found in one direction. This cleavage actually does not significantly influence fragment orientation. The crystals of Monticellite are commonly twinned. It may actually have cyclic twins on one plane. If it would appear euhedral, then it would look like a six-pointed star in cross section.
In optical mineralogy, the elongate cross sections of Monticellite may be either length fast or length slow depending on how they are cut. The trace of the cleavage is length slow but the cleavage is usually not visible. The indices and birefringence of Monticellite may increase in a linear manner with the addition of iron or manganese in the composition. The interference figure of Monticellite is biaxial negative as found clearly exhibited by the mineral under polarized microscope used in optical mineralogy.
Mineral Monticellite may be altered to serpentine or other calc-silicates and other related minerals. The distinguishing features of Monticellite usually include lower birefringence, cleavage, optic angle, and interference figure. Monticellite is usually found in contact metamorphosed or metasomatized siliceous dolomitic limestones. It is also most commonly adjacent to granitic intrusions. It can be also possibly found in mafic and ultramafic igneous rocks.
