The Trifari brooch above is made of yellow glass. A princess cut is a square-cut stone. This fancy cut is relatively new and is also known as a Quadrillion or Squarillion cut. Pt. is an abbreviation for platinum . Diamonds have a hardness of 10, a specific gravity of 3.5, and a refractive index of 2.417 - 2.419.
Marcasite stones come from pyrite.