EffJot

Callan Bentley asks what are the five most important minerals one should know about, and why – “if you had to introduce a non-geologist to just five of the earth's multitudinous building blocks, which ones would you choose to share?” Here's my list.

1. Quartz is a important component of a lot of rocks and very stable, so especially sands are mostly made up of quartz. (Think nice beaches, computer chips, and rich aquifers.)
2. Clay minerals¹ are formed by weathering of other silicates. Layers of clay are poorly permeable to water and act as aquicludes that confine and protect aquifers. They are able to adsorb (and desorb) ions on their surface and therefore play an important role for soil fertility. Also, poor permeability and sorption capacity make them useful for sealing waste landfills and the like.
3. Ice. Although I consider all forms of water extremely important, only ice is solid and crystalline and can therefore be called a mineral. Ice is a large reservoir of water, with an effect on climate, ocean water-levels and currents. Frost wedging can be a powerful weathering agent, and glaciers have substantially shaped large regions during the ice-ages.
4. Halite (NaCl). Salt is an essential mineral for animals (less so for most plants). Deeply buried salt beds become mobile under the pressure and can form salt domes that rise close to the surface and lift up the neighbouring rocks with them. Today, the domes are not only source of salt but sometimes also a sink for hazardous and nuclear wastes (not without problems, as seen recently in the Asse).
5. Calcite (calcium carbonate) is the main constituent of limestones, which can form large sedimentary formations. Carbonates dissolve quite easily, which can form – sometimes spectacular – karst landscapes and caves. But carbonate also affects the acid-base conditions of both soils and water. And it is an raw material for construction.

1. Considering that the aim is a introduction to an “outsider”, I think it's justified that I've cheated a bit and sneaked in a group instead of a single mineral. [↩]