How are the shapes of crystalsclassified?
Geometry plays an important part in the study of minerals. This is because certain
minerals exhibit specific shapes called crystals, with specific crystalline forms occur-
ring when a mineral’s atoms join in a particular pattern or internal structure. This
arrangement is determined by several factors, including the chemistry and structure
of the mineral’s atoms, or even the environment in which the crystal grew.
Overall, there are specific angles between corresponding faces of all crystals. Min-
eralogists (scientists who study minerals) divide these crystalline forms into 32 geo-
metric classes of symmetry; they use this information to identify and classify certain
minerals. The crystals are also subdivided into seven systems on the basis of an imagi-
nary straight line that passes through a crystal’s center (or axis). The seven groups
include cubic (or isometric), tetragonal, orthorhombic, monoclinic, triclinic, hexago-
nal, and trigonal (or rhombohedral). For example, a crystal in the cubic system has
three axes that intersect at right angles; the axes are also of equal lengths. The best
way to envision this crystal is to think of a box with equal sides—or a cube.
What is a carat?
A carat is a unit of measurement representing the weight of precious stones, pearls,
and certain metals (such as gold). It was originally a unit of mass based on the carob
seed or bean used by ancient merchants in the Middle East. In terms of weight mea-
surement, a carat equals three and one-fifth grains troy, and it is also divided into four 299
MATH IN THE NATURAL SCIENCES
A “dip” is the angle at which a layer of rock or vein is inclined, while a “strike” is the angle made between the
direction of true north and the direction of the planar feature, such as an incline or fault.