Metalloids are elements whose properties are intermediate between metals and solid nonmetals or semiconductors.
A variety of elements are often considered metalloids:
- boron, considered here in the boronides,
- aluminum, a face-centered cubic metal, considered in the aluminides,
- silicon, here in the siliconides,
- gallium (it can occur in the liquid state as a mineraloid),
- selenium, also included in the chalcogens,
- tellurium, also included in the chalcogens,
- polonium, considered as among the heavy metals and
- astatine, here is with the halogens.
Each of the metalloids, in the native or elemental form has at least one crystal structure, but these structures may not be the usual cubic structures: face-centered cubic or body-centered cubic that metals often occur in.
While native gallium would be the best source of gallium, it apparently does not occur on Earth.
Gallite (CuGaS2) is 25 at % gallium.
Native arsenic such as in the image on the right and at the top of this resource occurs in silver ore veins.
Allemontite is a native alloy of arsenic and antimony, with a composition of AsSb.
The first example on the right is from the mineral collection of Brigham Young University Department of Geology, Provo, Utah.
The second is from Příbram, Central Bohemia Region, Bohemia (Böhmen; Boehmen), Czech Republic.
As a natural source of arsenic, it has 50 at % arsenic.
On the right is a photograph of native selenium from the mineral collection of Brigham Young University Department of Geology, Provo, Utah.
The second image down on the right shows dark gray selenium in sandstone from Westwater Canyon Section 23 Mine Grants, New Mexico.
On the right are microprobe fragments of native indium from Eastern Transbaikal, Russia. The electron microprobe confirms that indium is the only component of the metallic phase.
Native tin such as in the images on the right occurs in two crystal forms: α-Sn (cubic) and β-Sn (tetragonal).
Native antimony such as occurs in the rock on the upper right with its various oxidation products is crystalline in the hexagonal system.
The second image shows hexagonal crystals with metallic luster.
On the right is an example of native tellurium from the Emperor Mine, Vatukoula, Tavua Gold Field, Viti Levu, Fiji.
- Traditional metalloid recovery processes applicable on Earth may not be so applicable on other astronomical objects such as Mars or the Moon.