Chemical substanceA chemical substance is a form of matter having constant chemical composition and characteristic properties. Chemical substances can be simple substances (substances consisting of a single chemical element), chemical compounds, or alloys. Chemical substances that cannot be separated into their simpler constituent elements by physical means are said to be 'pure'; this notion intended to set them apart from mixtures.
Hypothetical types of biochemistryHypothetical types of biochemistry are forms of biochemistry agreed to be scientifically viable but not proven to exist at this time. The kinds of living organisms currently known on Earth all use carbon compounds for basic structural and metabolic functions, water as a solvent, and DNA or RNA to define and control their form. If life exists on other planets or moons it may be chemically similar, though it is also possible that there are organisms with quite different chemistries - for instance, involving other classes of carbon compounds, compounds of another element, or another solvent in place of water.
SilicosisSilicosis is a form of occupational lung disease caused by inhalation of crystalline silica dust. It is marked by inflammation and scarring in the form of nodular lesions in the upper lobes of the lungs. It is a type of pneumoconiosis. Silicosis (particularly the acute form) is characterized by shortness of breath, cough, fever, and cyanosis (bluish skin). It may often be misdiagnosed as pulmonary edema (fluid in the lungs), pneumonia, or tuberculosis. Using workplace controls, silicosis is almost always a preventable disease.
Black lung diseaseBlack lung disease (BLD), also known as coal-mine dust lung disease, or simply black lung, is an occupational type of pneumoconiosis caused by long-term inhalation and deposition of coal dust in the lungs and the consequent lung tissue's reaction to its presence. It is common in coal miners and others who work with coal. It is similar to both silicosis from inhaling silica dust and asbestosis from inhaling asbestos dust. Inhaled coal dust progressively builds up in the lungs and leads to inflammation, fibrosis, and in worse cases, necrosis.
Planetary protectionPlanetary protection is a guiding principle in the design of an interplanetary mission, aiming to prevent biological contamination of both the target celestial body and the Earth in the case of sample-return missions. Planetary protection reflects both the unknown nature of the space environment and the desire of the scientific community to preserve the pristine nature of celestial bodies until they can be studied in detail. There are two types of interplanetary contamination.
ChalcedonyChalcedony (kælˈsɛdəni , or ˈkælsəˌdoʊni ) is a cryptocrystalline form of silica, composed of very fine intergrowths of quartz and moganite. These are both silica minerals, but they differ in that quartz has a trigonal crystal structure, while moganite is monoclinic. Chalcedony's standard chemical structure (based on the chemical structure of quartz) is SiO2 (silicon dioxide). Chalcedony has a waxy luster, and may be semitransparent or translucent.
