A material that has been heated to a temperature above its (normal atmospheric pressure) boiling point, but which is kept in a state that resembles a liquid via the application of high pressure. For example, water will remain “liquid” up to a temperature of 375°C (617°F) if it is placed under enough pressure. Ammonia will remain “liquid” up to a temperature of 133°C (271°F) if it is placed under enough pressure, despite the fact that ammonia normally becomes a gas (at std. atmospheric pressure) whenever the temperature is higher than -33.35°C (-30°F). These supercritical fluids have unique properties (e.g., they are often better solvents than their true liquid forms). Some supercritical fluids (e.g., supercritical carbon dioxide) can be used to extract biological molecules (e.g., chlorophyll) from mixtures (e.g., ground up plant leaves). After the biological molecule has dissolved out of the mixture, the biological molecule is recovered by releasing pressure so the carbon dioxide returns to gaseous form, and drifts away.