grains (sometimes referred to as carat
grains). Diamonds and other precious
stones are estimated by carats and frac-
tions of carats; pearls are usually mea-
sured by carat grains (for more about
grains and measurement, see “Mathemat-
ics throughout History”).
Carats of gold are measured based on
the number of twenty-fourths of pure
gold. For example, 24-carat gold is pure
gold (but for a goldsmith’s standard, it is
actually 22 parts gold, 1 part copper, and
1 part silver, as real gold is too malleable
to hold its shape), 18-carat gold is 75 per-
cent pure, 14-carat gold is 58.33 percent
pure, and 10-carat gold is 41.67 percent
pure gold.How is modeling and simulation
used in geology?
Like so many other fields of science, mathematical modeling and simulation is used in
geology to understand the intricacies of physical events in the past, present, and future.
For example, hydrologists (geologists who study water flow above and below the Earth’s
surface) often use models to simulate the effects of increased groundwater pumping of
wells. They may also use a simulation to determine how much water can be presently
pumped out of a well, or how much can be pumped out in the future without harm to
the environment. Other hydrologists may use modeling to understand the flow of water
in a river, bay, or estuary, for example, to determine how the water erodes a shoreline.
Still other researchers may model how snow on a volcanic mountain melts, gathers
debris, and potentially flows toward populated areas during an eruption event. (For
more about modeling and simulation, see “Math in Computing.”)How do geologists measurethe intensity of earthquakes?
Geologists measure the intensity of earthquakes in order to compare and judge poten-
tial damage. One of the first standard ways to measure intensity was developed in 1902
by Italian seismologist Giuseppe Mercalli (1850–1914) and is called the Mercalli Inten-
sity Scale (it was later modified and renamed the Modified Mercalli Intensity Scale).
The numbers, in Roman numerals from I to XII, represent the subjective measure-
ment of an earthquake’s strength based on its effects on local populations and struc-
300 tures. For example, Roman numeral V on the scale represents a quake felt by nearly
The geometric arrangement of molecules within the
mineral determines the shapes of its crystals. The
Image Bank/Getty Images.