that contains fluorine and calcium. Fluorite can be found in many colors. If you shine an
ultraviolet light on some samples of fluorite, they will glow!
Oxides
Earth’s crust contains a lot of oxygen, which combines with many other elements. Oxides
are minerals that contain one or two metal elements combined with oxygen. Oxides are
different from silicates because oxides do not contain silicon. Many important metals are
found as oxides. For example, hematite and magnetite are both oxides that contain iron.
Hematite (Fe 2 O 3 ) has a ratio of two iron atoms to three oxygen atoms. Magnetite (Fe 3 O 4 )
has a ratio of three iron atoms to four oxygen atoms. You might have noticed that the word
magnetitecontains the wordmagnet.Magnetite is a magnetic mineral.
Figure 3.9: Magnetite ( 12 )Phosphates
Phosphates have a tetrahedron building block that is similar to that of the silicates. But,
instead of silicon, phosphates have an atom of phosphorus, arsenic, or vanadium bonded
to oxygen. Although there are many minerals in this group, most of the minerals are rare.
The chemical composition of these minerals tends to be more complex than some of the
other mineral groups. Turquoise is a phosphate mineral that contains copper, aluminum,
and phosphorus. It is rare and is used to make jewelry.