Calcite, the most common form of natural calcium carbonate (CaCO3), a widely distributed mineral known for the beautiful development and great variety of its crystals.
A wavefront is a surface over which an optical wave has a constant phase. For example, a wavefront could be the surface over which the wave has a maximum (the crest of a water wave, for example) or a minimum (the trough of the same wave) value. The shape of a wavefront is usually determined by the geometry of the source.
When we think of the word wave we usually picture someone moving their hand back and forth to say hello or maybe we think of a curling wall of water moving in from the ocean to crash on the beach. In physics, a wave is a disturbance that travels through space and matter transferring energy from one place to another.