Lab-created fire opal is synthetic gemstone NOT PLASTIC. Elements:80% Silica & 20% Resin. MOHS hardness:4. Specific Gravity:1.80-1.90. Heat Resistance:130 degree C. Lab-grown synthetic opal takes about a year to grow in laboratory and is similar in properties to natural opal. Lab-grown synthetic opal contains high percentage of silica at least 80% and has the unique feature of vertical growth pattern. Silica is an important element for opal. According to GIA in order to be opal a material must be silica in composition as major elements possibly containing some water. the percentage of silica in composition determines man-made opal's quality and value. Lab-grown synthetic opal is also known as created opal or lab-made opal or lab-created opal.