Little school of mineralogy – 5
What are native elements and how common are they in nature?
Minerals that occur as elements are called native elements and are very rare in nature.
About twenty minerals are known to belong to the class of native elements, and they make up approximately 0.1% of the total mass of the Earth’s crust.
The reason for their rare occurrence in nature is that the vast majority of chemical elements easily form compounds.
What does the class of native elements include and what are their main characteristics?
The class of native elements includes metals, metalloids and non-metals.
Native metals are built as densely packed arrangements of atoms connected to each other by metallic bonds.
They most often crystallise in the cubic or hexagonal system and have many common physical properties such as metallic lustre, high density, and good thermal and electrical conductivity.
Unlike metals, native metalloids are brittle and cannot be forged, but they have a metallic lustre. They crystallise in the hexagonal system, and due to their layered structure they are characterised by good cleavage.
Minerals from the group of native non-metals are few in number and differ greatly from one another.
Which minerals are the main representatives of the native elements class?
The best-known native elements from the group of metals are: gold, silver, copper, platinum, iron and mercury; from the group of metalloids, arsenic, antimony and bismuth; and from the group of native non-metals, diamond, graphite and sulphur.
What do diamond and graphite have in common, and how do they differ?
Diamond and graphite are allotropic modifications of the same chemical element – carbon, C, so the chemistry of these two minerals is the same.
However, they differ in their internal structure, that is, in the arrangement of carbon atoms within the structure.
In the structure of diamond, each carbon atom is connected by strong covalent bonds to four neighbouring atoms arranged at the vertices of a tetrahedron, while in the structure of graphite each carbon atom is connected to three neighbouring atoms arranged in the same plane, forming layers that are weakly connected to one another.
Consequently, these two minerals differ significantly in their physical properties, such as form, colour, lustre, cleavage and especially hardness.
DIAMOND – C
The name is derived from the Greek word adámas, meaning invincible, synonym alem stone.
Non-metal; cubic modification of carbon; common crystals with developed faces of octahedron, hexahedron, rhombic dodecahedron or tetrahedron, with faces often curved; transparent; most often colourless, but due to impurities it may be black, red, yellow, blue, grey, brown or green.
It has a white streak, which due to its great hardness is determined by crushing it into powder; adamantine lustre; perfect cleavage along the octahedral face; conchoidal fracture; hardness 10, the hardest – 10th mineral on the Mohs hardness scale; density 3.5 g/cm3.
GRAPHITE – C
The name is derived from the Greek word graphein, meaning to write.
Non-metal; hexagonal modification of carbon; common flaky or earthy aggregates, rarer thin-platy hexagonal crystals; opaque; dark grey to black colour, black streak; metallic to earthy lustre; perfect cleavage along the basal pinacoid face; uneven fracture; hardness 1 – 2, because of its low hardness graphite is used for writing; density 2.2 g/cm3.
Prepared by: Biserka Radanović-Gužvica