Endangered element: indium

Unlike others in the endangered element series, indium use is not dominated by a single application—indium is employed in a number of applications.  For example, the screen you are looking at contains indium in the form of ITO—indium tin oxide—whose semi-conductive properties make it useful for controlling liquid-crystals.  Indium semi-conductors are also useful for thin-film solar panels, LEDs, and electroluminescent materials.  It is also found in solder, sodium vapor lamps, and nuclear control rods.  Truly, it's a versatile metal.

However, indium is relatively rare.  It comprises only 50 parts per billion (ppb) of the Earth's crust. One author compares indium with silver, claiming that silver is less abundant yet produced in higher quantities.  However, silver comprises 70 ppb of the Earth's crust—still quite rare, but about as common as indium.  Furthermore, silver is commonly found in ores, such as argentite.  Indium minerals are uncommon.  Instead, it is extracted from sphalerite—zinc ore—where it has a concentration of 1 to 100 parts per million.  Fortunately, there has been substantial interest in finding substitutes for indium.  Many of these solutions, however, still rely on non-renewable resources, like petrol chemicals or other endangered elements—e.g. gallium arsenide.

Rare metals

Our society is dependent on an abundance of mineral resources.  You are reading this today, because of a number of rare metals that have been used to construct the computer—or tablet, smart phone, etc.  A large amount of time and effort is spent discovering, extracting, and transporting these materials from the Earth.  Let's consider four of them: zinc, gallium, indium, and hafnium.  These are example of so-called endangered elements.

Composition of the Earth's crust.

As much as 95% of the Earth's crust is composed of silicates—minerals that contain silicon and oxygen.  These minerals are not as suitable as the remaining 5% as ores, because the chemical bonds of silicates require more energy to be broken.  However, even a pessimistic calculation estimates that there may be 10 quadrillion tonnes of non-silicates accessible to human mining efforts.

Ores are important for two reasons.  First, they feature higher concentrations of certain elements than the rest of the Earth's crust—often, much higher concentrations.  Second, their chemical purity make them suitable to industrial processes.  Zinc is only the 25th most abundant element in the Earth's crust, but readily bonds with sulphur in an ore called sphalerite.  It comprises 79 parts per million (ppm) of the Earth's crust, which is more abundant than silver, gold, or even copper.  Gallium, indium, and hafnium are not typically obtained from unique ores, but occur in trace amounts in other metals.  They are also substantially rarer at 17 ppm, 49 parts per billion (ppb), and 5 ppm, respectively.

These elements in particular have applications to technologies that will be important during the next century, and will likely experience growing demand in the face of dwindling supply—which would adversely affect their price, and the prices of technologiey.