Let’s learn about the common minerals that make up river and beach sand (and non-mineral grain such as lithic fragments)
A common mineral, present in many rock types. Quartz looks similar to feldspars (see below) by the naked eye, but doesn’t weather as feldspars does and is translucent. Large, transparent examples are called rock crystal. Normally colorless, quartz crystals may contain small amounts of impurities that produce shades of purple, light brown, or pink.
The most common mineral, present in almost all rock types, plagioclase makes up approximately 50% of the Earth’s crust. Colorless and translucent, it can become milky through weathering. Since it is almost impossible to differentiate plagioclase from potassium feldspar with the naked eye, they are sometimes lumped together and simply called “feldspar.”
Feldspar containing potassium, this mineral is frequently found in granite. It is difficult to differentiate it from plagioclasewith the naked eye. They sometimes appear similar under the microscope as well.
Common in volcanic sand (ash); gray-brown to brown color and bladed crystal shapes are characteristic.
Also common in volcanic sand (ash); green color and bladed crystal shapes are characteristic
A huge variety of amphiboles exists, the most common being hornblende, which is dark green to black in color and prismatic in crystal form, prolate in sand grains. Their dark, concentrated color often makes amphibole particles appear opaque.
A familiar gemstone characterized by its red color and rounded, equant form, garnet is often found in granite, metamorphic rocks, and sandstone.
Formed of stacks of papery sheets, muscovite is colorless, with a sparkly sheen. While it is classified as a heavy mineral, its crystal shape may enable it to float. Muscovite is primarily found in granite and metamorphic rocks.
Apart from its dark brown color, biotite is identical to muscovite; it too is found in granite and metamorphic rocks.
The most abundant constituent of the earth’s mantle, olivine is uncommon in the crust. Yellow-green, it usually occurs in rounded, equant form. Transparent, gem-grade olivine is known as peridot.
Light yellow-green and prismatic in form, epidote is found primarily in metamorphic rocks.
Shiny, black, and opaque, magnetite occurs in nearly perfect octahedrons (though some may have slightly rounded corners). Strongly magnetic, it will stick to an ordinary standard magnet.
Pyrite occurs mainly in cubic in form and is opaque, but it has a golden metallic luster. Can be easily differentiated from magnetite with a magnet, because it is non-magnetic.
Glass formed in a volcanic eruption, nominally translucent but frequently milky in appearance by alteration, some volcanic glasses are porous, and may appear rough surfaces.
Occurring in many colors, from white to gray, black or even green, lithic fragments are opaque, with no set shape.
While extremely rare, natural gold is sometimes found in sand. Opaque, with a dull metallic luster, these particles have no set shape and are extremely dense compared to other minerals. Silver and other metals are also discovered on occasion. If you search carefully downstream from a mine, you might get lucky.
At times, man-made metals, plastics, glass, or ceramics may be mixed into sand. Though sometimes appearing similar to natural particles, most man-made objects can be identified by their rough, irregular shapes and gaudy colors.
