Saturday, 29 October 2011

What is meant by some of these names (1)

I have a habit of blasting people with technical jargon sometimes and I keep forgetting that I'm a bit of a geology geek and sometimes I'm hard to understand. So I thought it might be wise to have a quick comment on some of the names that I use. There are many different types of geological names. The main types (in my opinion) are:

1. geological ages;
2. mineral names;
3. rock names; and
4. rock unit names

But just to complicate things each of these can be broken up with further names for instance:

Geological ages from the International Stratigraphic Commission.
1. geological ages: the age Cenozoic era (65.5 million years to the present) includes smaller age periods called the Quaternary (present to 2.6 million years ago), Neogene (2.6 million years to 23 million years) and Paleogene (23 million years to 65.5 million years) periods. These too can be subdivided.

2. mineral names: minerals like quartz and feldspar will be familiar to most since they are the two most common minerals on earth but these can be broken down further based on slightly different chemical properties. Feldspar can also be called plagioclase (if it is richer in the elements sodium and calcium - [chemical formula NaAlSi3O8 to CaAl2Si2O8]) or orthoclase (if it is richer in the element potassium [chemical formula KAlSi3O8]). Needless to say, these mineral names too can be subdivided.

3. rock names: you've probably heard of basalt but what about hawaiite, mugarite, tholeiite and benmorite? Well, these are just fancy names for different basalts based on slightly different mineral compositions. E.g. tholeiite has quartz (due to higher silica) and hawaiite has olivine (due to low silica). Thank goodness, these basalts are rarely subdivided any further.

4. rock unit names: One I will refer to regularly on this blog is the Lamington Volcanics. This is a unit that refers to all the rock sourced directly from the Tweed Volcano (Mount Warning area) and the Focal Peak Volcano (Mount Barney area). Itself it contains sub-units such as the Lismore Basalt which is mainly comprised of basalt (mainly of the tholeiite type) that was erupted during the Cenozoic era (Neogene to Paleogene periods). Yes, some of these units can further be subdivided.

When you get right into geology it becomes evident that it can be quite tricky. But most of the trickiness comes from learning all the names not from understanding what actually happens with rocks! I will continue to occasionally post on nomenclature in the future. In the mean time you may find some help in the glossary.

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