of about $1 a gram. All the above methods yield adamantane as a polycrystalline powder. Using this powder, single crystals can be grown from the melt, solution, or vapor phase (e.g. with the Bridgman–Stockbarger technique). Melt growth results in the worst crystalline quality with a mosaic spread in the X-ray reflection of about 1°. The best crystals are obtained from the liquid phase, but the growth is impracticably slow – several months for a 5–10 mm crystal. Growth from the vapor phase is a reasonable compromise in terms of speed and quality. Adamantane is sublimed in a quartz tube placed in a furnace, which is equipped with several heaters maintaining a certain temperature gradient (about 10 °C/cm for adamantane) along the tube. Crystallization starts at one end of the tube, which is kept near the freezing point of adamantane. Slow cooling of the tube, while maintaining the temperature gradient, gradually shifts the melting zone (rate ~2 mm/hour) producing a single-crystal boule. Natural occurrence Adamantane was first isolated from petroleum by the Czech chemists S. Landa, V. Machacek, and M. Mzourek. They used fractional distillation of petroleum based. Landa et al. could produce only a few milligrams of adamantane, but noticed its high boiling and melting points. Because of the (assumed) similarity of its structure to that of diamond, the new compound was named adamantane. Petroleum remains a source of adamantane; the content varies from between 0.0001% and 0.03% depending on the oil field and is too low for commercial production. Petroleum contains more than thirty derivatives of adamantane. Their isolation from a complex mixture of hydrocarbons is possible due to their high melting point and the ability to distill with water vapor and form stable adducts with thiourea. Physical properties Pure adamantane is a colorless, crystalline solid with a characteristic camphor smell. It is practically insoluble in water, but readily soluble in nonpolar organic solvents. Adamantane has an unusually high melting point for a hydrocarbon. At 270 °C, its melting point is much higher than other hydrocarbons with the same molecular weight, such as camphene (45 °C), limonene (−74 °C), ocimene (50 °C), terpinene (60 °C) or twistane (164 °C), or than a linear C10H22 hydrocarbon decane (−28 °C). However, adamantane slowly sublimes even at room temperature. Adamantane can be distilled with water vapor. Structure As deduced by electron diffraction and X-ray crystallography, the molecule has Td symmetry. The carbon–carbon