A mineral is a naturally occurring chemical compound. The most abundant minerals on Earth are feldspar_ (50%) and then quartz_ (12% of the Earth's crust).

A stone (= rock) is a solid aggregate of one or more minerals. For example, chalk_, coal_, flint_, fluoride, granite_, lapis lazuli_, limestone_, marble_, pumice_, sandstone_, slate_.


1   Minerals

Fluoride is a mineral. It is estimated to be the 13th most abundant element in the Earth's crust, and can be found in natural sources of water.

2   Function

Sand can melted to form glass. When lightning strikes sand it often forms glass.

3   Properties

3.1   Angle of repose

Sponateneous stratification from pouring granular mixtures.

Typically pouring stuff together results in further mixing, yet here the result is an ordered sorting into layers. The larger rounded dark grains separate from the smaller sharp-edged white grains forming the layers you see here. The darker grains alone would stack into a steeper pile (larger angle of repose) than the white which would form a less steep pile. An amazing physics discovery of the 1990s showcased here by Ken Brecher and Erik Thogerson.

Basically angle of repose is the steepest a pile of material can pile before it spreads out. Sharp-edged grains "catch" onto each other more easily, and can be stacked at a steeper angle. The dark grains are likely sharper, and the white grains are probably rounder. So the white grains want to roll down more quickly.

4   Substance

Rocks are composed of grains of minerals, which, in turn, are homogeneous solids formed from a chemical compound that is arranged in an orderly manner. The aggregate minerals forming the rock are held together by chemical bonds. The types and abundance of minerals in a rock are determined by the manner in which the rock was formed.

5   Classification

Rocks can be classified into three classes: igneous rocks (granite_), sedimentary rocks, and metamorphic rocks (marble_).

Boulder > cobble > gravel > sand > silt > clay.

By grain size: Sand is a granular material composed of sand grains ranging in diamater from 1/16 mm to 2 mm. Gravel ranges from 2 mm to 64 mm. Silt has particles between 0.004 mm and 1/16 mm.

6   Market


After air and water, sand is our most used natural resource. (By what metric?) We use it to make food, wine, toothpaste, glass, computer chips, breast implants, cosmetics, paper, paint, and plastics.

Marine sand is the and that you find at the bottom of rivers, on beaches, and at the bottom of lakes and oceans. We can't use sand from the desert; wind erosion makes the grains too round for most purposes. We need angular sand that locks together likes pieces of a puzzle.

The major player for sand usage is concrete. Concrete is made of 10 percent cement, 15 percent water, and 75 percent sand. The concrete required to build a house takes on average about 200 tons of sand. A mile of highway requires 15,000 tons.

Since the world makes over 4 billion tons of concrete annual, we need more sand every sand every year. Especially since cities are growing, especialyl in the developing world.

China outpaces the world in cement production by a lot: 2,500 metric tons in 2014. (In 2014, India produced 280 metric tons, and the US produced 83 metric tons.) Between 2011 and 2013, China used 6.5 gigatons of concrete, more than the 4.5 tons of concrete the United States used in the entire 20th century. Most of the sand comes from dredging Poyang Lake. 236 million cubic meters of sand are dredged every year, making it the largest single sand mine in the world. China is also using sand to build up island in the South China Sea.

Artifical island in Dubai required 186.5 million cubic meters of sand. This depelted the sea floor, so sand had to be imported from Austraila. Sand extraction is a $70 billion dollar industry.

The cheapest and best quality sand comes from river beds. You send out a boat into the middle of a river with a big suction pump. However the sand isn't very deep. Sand is a thin layer over rock. That layer is home to organisms which feed the base of the food chain. Collecting all that sand disrupts fishing in the area and the landscape on shore; removing sand from the seabed causes the shore to slide into the water. This can make flooding worse.

The price of sand has gone up 5x in the last 30-40 years. That may explain one of the reasons the cost of housing has gone up.

It is possible to create sand by crushing rocks and recycled concrete. Glass bottles can also be ground up to make sand to replenish beaches.

7   References

[1]Tech Insider. June 6, 2018. World Is Running Out Of Sand — Why There's Now A Black Market For It. https://www.youtube.com/watch?time_continue=37&v=E0jfn61FTGQ