1) Haematite. This is a mineral (a natural oxide of iron) it also serves as a major ore of iron and can be cut into attractive shapes to use as a gemstone.
Sphalerite. This is a mineral (a natural sulphide of zinc) it is also a major ore of zinc. Pure sphalerite can be fashioned into very beautiful gems but these are only for collectors as the softness and easy cleavage of sphalerite make it quite unsuitable for mounting in jewellery.
Diamond. This is a Native Element (to fit the definition of a mineral a substance has to be naturally occurring chemical COMPOUND which diamond is not) It is mounted directly into industrial tools due to its hardness but cannot be thought of as an ore. It also is cut into a range of exquisite gems.
2) Most quartz is not considered a gemstone because it lacks qualities important in jewelry, such as color intensity and clarity. The bulk of quartz on earth is contained in milky white veins, massive granite, quartzite formations, and sands. And not all colored quartz like agate, amethyst, or jasper is gem-quality. Even these come in different grades, determined by color intensity, internal patterns, clarity and ability to take a polish.
3) It is non-toxic, durable and lightweight.
4) All gems are minerals, but not all minerals are gems. In order for the mineral to be classified as a gem, the mineral must have very specific qualities.
5) Many ores are found in vein mineral deposits. These deposits form when ions of metals dissolve in fluids and collect in weak parts of rock, such as cracks and surfaces between layers. To remove the ore, miners also must remove the surrounding waste rock.
