Petroleum Included Quartz Crystal - Fluorescent Bituminous Hydrocarbon Inclusions in Herkimer Type Quartz
Photos  in UV-SW , UV-LW and natural light
Almost all quartz crystals contain small amounts of fluids in inclusions, but usually the cavities are microscopically small. Many rock crystals have a cloudy or milky base because of myriads of small bubbles included. Even the quartz grains in granite contain fluids, although the granite has formed from an at least partially molten rock.
Water is the most common inclusion, as most quartz crystals grew in a watery solution in a hydrothermal environment. Some quartz contains higher carbohydrates, like raw petrol and bitumen. But carbon dioxide, CO2, and methane, CH4, can be found as well. Although both are gases at normal pressure, they have been enclosed as liquids at very high pressures during crystal formation.

A branch of mineralogy has specialized in studying fluid inclusions, and the favorite material is quartz, as it is chemically stable in a broad range of environments and fluids, gases and solid materials that have been enclosed during crystal growth are almost perfectly sealed and preserved. Studying the fluid inclusions helps to reconstruct the chemical and physical conditions during rock formation.

Besides that, some fluid inclusions are fascinating even to people who do not collect minerals or know anything about them: those that are large and contain a small gas bubble that moves about when the crystal is turned are among the favorites on fairs (finally a stone that "does something"...).

Watery inclusions are frequently found in skeleton quartz. They are trapped by quickly growing crystal faces that grow from the edges to the center.

The gas bubbles form when the quartz cools, as petroleum is less dense it contract more than the qiartz and creates a vacuum with the petroleum included inside