There are three different Mexican Fire Opal Pendants avaible. Please note the measurements are approximate and they are already set in a silver setting. A chain will be included in your purchase. 
A: 17 x 21 mm: thickness is 7 mm: weight is 9 grams
B: 12 x 19 mm: thickness is 8 mm: weight is 6 grams
C: 17 x 21 mm: thickness is 4mm: weight is 6 grams
 
Mexican Fire Opal holds a red through yellow to colorless body color caused by traces of iron. Opals form over hundreds of years from within antiquated water routes as microscopic layers of silica spheres settle on top of one another. Mohs is 6-6.5.