Definition: Allactites are a type of granite that varies in color, texture, and chemical composition. The term "allactite" comes directly from the Greek words "alkaite," which means "black stone," and "tisla," meaning "granite." It is characterized by its black or brownish gray appearance, with a grain-like surface, often resembling an agate. Allactites are typically found in the middle and upper layers of granite. They are not typically found at the surface of granite, which makes them less common compared to other types of granite. Allactites are not typically affected by weathering or alteration processes like gabbro or diabase, due to their black nature. Allactites are composed mostly of calcium oxalate (Ca(OH)2), a mineral found in the earth's crust. The specific chemical composition varies but can include elements such as Ca, Al, Mg, K, and Si, which can affect their properties depending on the depth and texture. The term "allactite" is often used to refer to all types of black granite or marbles. It can be found in many different regions around the world, from southern Europe to the United States.

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