Synthetic gemstones are manufactured in laboratories under controlled temperature and pressure conditions. They are man-made recreations of their natural counterparts, possessing essentially the same physical and chemical properties and crystalline structure. Material that simulates or imitates a specific gemstone, but of which the chemical and physical properties are entirely different from the simulated gemstone, is known as a simulant, e.g. green glass simulating emerald. Any stone constructed of two or more parts of gem material, whether they be natural, synthetic, imitation or any combination, is referred to as a composite or assembled stone, e.g. an opal triplet.