Spectrolite is a hard and rare variety of labradorite feldspar. Spectrolite is between 6 and 6.5 hardness and weighs 2.69 - 2.70 g/cc. Spectrolite was discovered by the Finns during WWII when building a defense line. After the war, spectrolite was mined in small quantities. This small supply made it more valuable. Feldspar is the name of an important group of rock-forming minerals which make up perhaps as much as 60% of the Earths crust. ... In materials science, hardness is the characteristic of a solid material expressing its resistance to permanent deformation. ... Density (symbol: ρ - Greek: rho) is a measure of mass per unit of volume. ... Combatants Allied Powers Axis Powers Commanders {{{commander1}}} {{{commander2}}} Strength {{{strength1}}} {{{strength2}}} Casualties 17 million military deaths 7 million military deaths World War II, also known as the Second World War (sometimes WW2 or WWII), was a mid-20th century conflict that engulfed much of the globe and is accepted as...