Colour coding:



Rock cycle index

The Rock cycle

Rock formation

Erosion and weathering

Identification of rocks



Crystal structures of rocks






Magnetite: its macroscopic piramidal form reflects its octahedral crystalline structure



Ores - The rocks that are the source of metals

Most metals we use are not found in native form. They come from rocks.

These rocks, called ores, are submitted to a process called smelting, so that the metals are extracted. The metal atoms are usually bound to oxygen (oxides) or sulphur atoms (sulphides), among other elements.

For instance, gold often comes about bound to sulphur. Gold mines also produce a lot of sulphur. The gold mine close to BH (Brasil) has also a sulphuric acid plant to make use of the sulphur produced as a byproduct of the gold mining.

Below we see crystal structures of such rocks (ores):

Iron ores

magnetite crystal structure

Magnetite - Fe3O4

The name comes from its magnetic properties!

Both golden and green atoms represent iron. The green

colour is used to show tetrahedral sites and golden represent octahedral sites. This interesting structure can be explored further on the animation.


hematite crystal structure

Hematite - Fe2O3


Copper ores

Cuprite - Cu2O


Chalcopyrite  crystal structure

Chalcopyrite - CuFeS2



Mercury ore


cinnabar crystal structure

Cinnabar - HgS


Titanium ore

rutile crystal structure


Rutile - TiO2


Aluminium ore

cryolite crystal structure

Cryolite - Na3AlF6


Cromium ore

Chromite - FeCr2O4

Cr atoms represented in pink.

This structure can be further explored in the animation.