The chemical formula of Lawsonite is indicated by CaAl2Si2O7(OH)2-H2O. Lawsonite 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. It is also found having biaxial positive figure when viewed under polarized light microscope. The indices of the mineral are found in the range of about 1.665 to 1.686. The birefringence of the mineral is usually found 0.020. The optic angle of the mineral is within the range of 76 degree to 87 degree. When viewed closely under petrographic polarizing light microscope, Lawsonite is usually found exhibiting a moderately high positive relief.

 

            The hardness measure of Lawsonite is usually 8 when evaluated using the Mohs scale method. The specific gravity measure of the mineral is within the range of about 3.05 grams per cubic centimeters to 3.12 grams per cubic centimeters. If evaluated in hand sample, Lawsonite is commonly found colorless, white, bluish green, or bluish gray. When rubbed on a white porcelain streak plate, Lawsonite is most commonly found leaving a white streak. When evaluated in reflected light of polarized microscope, Lawsonite is commonly found exhibiting a vitreous to greasy luster.

 

            Lawsonite is usually found colorless in thin section and sometimes found weakly colored and pleochroic when viewed under petrographic polarizing light microscope. Lawsonite fragments in grain mount and thick sections are colorless or pleochroic. Lawsonite crystals are commonly found tabular in form with a prismatic cross section. When closely examined with the aid of petrographic polarizing microscope, Lawsonite cross sections are usually rhomb shaped or rectangular. Lawsonite is also found as anhedral grains or granular masses. It is occasionally found acicular.

 

            Lawsonite has two perfect cleavages that are pinacoidal and they intersect at right angles. There are also another two imperfect cleavages parallel to the prism faces that intersect at about 67 degree. The cleavage of Lawsonite tends to control the orientation of the fragments in grain mounts. Lawsonite crystals are commonly twinned as found clearly exhibited when viewed with the aid of the petrographic polarizing light microscope. Lamellar twinning with twin planes parallel to the prism face is the most common.

 

            The extinction of the rhombic section of Lawsonite is symmetrical with the slow ray vibrating parallel to the long diagonal. Rectangular sections of Lawsonite are length fast with parallel extinction. Cleavage fragments that are also length fast are found elongate parallel to the c axis. The ones that are elongate to the b axis are length slow. There is a little variation in the indices of refraction of mineral Lawsonite. The same is thru with its birefringence. The interference colors of Lawsonite in standard thin section ranges up to first-order red. The cleavage fragments of mineral Lawsonite lying on the cleavage plane is usually found yielding an acute bisectrix figures with large optic angle. The optic axis dispersion is usually found strong. Lawsonite mineral can be possibly replaced by pumpellyite as the result of metamorphic mineral reactions. It can be found as a common mineral in glaucophane schists and related low-temperature-high-pressure metamorphic rocks. It can be also found in metamorphosed gabbro, diabase, and related mafic rocks. Lawsonite is also occasionally present in marble and chlorite schists.