A metamorphosed basalt, typically submarine in origin, which contains chlorite in lieu of augite and olivine, and albitised feldspar. The change in the shape or volume of a rock body as a result of stress and which may be in the form of dilation or distortion, or both. Roughly, the change in a dimension or volume divided by the original dimension or volume. A joint which opens as a result of tension forces that developed during deformation. It normally becomes filled with quartz or other hydrothermal minerals.
Many tourmalines display colour zoning.
Small spherical or ellipsoidal cavities in a magma which are produced by bubbles of escaping gas formerly trapped during the solidification of lava.