glassy igneous rocks low in silica, such as basalt or diabase. Tachylytes are black with a pitchlike or resinous lustre; in thin sections they are ... [1 related articles] Found on http://www.britannica.com/eb/a-z/t/2
Tach'y·lyte noun [ Greek tachy`s quick + ... to dissolve.] (Min.) A vitreous form of basalt; -- so called because decomposable by acids and readily fusible. Found on http://www.encyclo.co.uk/webster/T/3