Crystals And Crystallization
To most people, a crystal is a sparkling gem-like solid with well-formed faces and a geometric shape. For many scientists, including mineralogists crystal and crystalline also refer to any solid compound having an ordered, repetitive, atomic structure. The atomic structure may or may not result in flat crystal faces and a gemmy appearance. We use the term crystal in both ways. When a mineralogist refers to a quartz crystal, the reference is usually to a six-sided prismatic shape with pyramidal ends. On the other hand, petrologists and mineralogists may refer to crystals of quartz in a rock such as granite. Such crystals rarely have perfectly developed smooth faces. All minerals are crystalline by definition, but perfectly formed crystals are rare. When faces on a mineral are flat and fully developed, giving the mineral a geometric shape, We say the crystal is euhedral. When no crystal faces are visible, We say it is anhedral. Those minerals that fall in between are subhedral.