Rocks and Minerals

A mineral can be defined as; a naturally occurring, inorganic, solid element or compound with a definite chemical composition and a regular internal crystal structure.

Rocks on the other hand can be made up of a single mineral but are generall made up of 2 or more minerals.  Have a look at this granite (made up of 3 minerals).

What are some of the characteristics that assist with identifying minerals include cleavage.  This refers to the way the crystals split.  Some examples are below.

Another characteristic is lustre.  This refers to how the mineral reflects light and its surface appearance.  Some of the categories are below.

Metallic: very high reflectance, opaque 
Sub-metallic: medium reflectance, opaque 
Adamantine: very high reflectance, transparent 
Glassy: high reflectance, transparent or translucent 
Resinous: medium reflectance, translucent 
Waxy: medium reflectance, translucent or opaque 
Pearly: low reflectance, translucent or opaque 
Dull: no reflectance, opaque


Mohs hardness scall is a useful classification tool.  The items listed below are reference materials,  If your material scratches the reference material, it is harder than that substance.  If the reverse happens then you material is softer than the reference substance.

Colour is unreliable for mineral identification in some circumstances.

Density of specific gravity of a mineral is also a useful tool.

Proxy data

What is proxy climate data?

Proxy climate data is an indirect measure or estimate of what the climate was like by indirect measurements (not with a thermometer or other instrument).  Most proxy data substitutes for direct data that predates accurate temperature measurements either locally or globally.

Direct measurements date back to the invention of reliable thermometers.  Countries with strong naval histories tend to be the earliest recordings of weather and temperature.  Accurate thermometers became available in the 18th century.

There are 2 ways historical climate can be determined.  The first way is by accessing tree rings.  This type of proxy data is useful for looking at local climates in terms of either temperature or rainfall patterns.  The dark regions or rings are usually associated with winter growth with the light ones being summer growth.  A large gap between dark rings indicates good growing conditions while narrow gaps indicate poorer growing conditions.

Ice core sampling produces alternating light (summer snowfall) and dark (winter snowfall) bands.  The thickness of the layers is a good indicator of temperature.  In addition, gas bubbles trapped in the layers can be extracted and tested to see what the atmosphere was like at the time of deposition.


This has led to some alarm owing to the rapid rise of CO2, a result of burning fossil fuels for just over 200 years.  When CO2 levels and estimated temperatures are compared, there appears to be a strong link.  The spike in CO2 in recent times is unprecedented for the last 500,000 years.  This is causing considerable debate now as groups argue for and against the link of CO2 and global warming.

Carbon "Locked Away"

One of the things that stromatolites and other photosynthetic organisms have done over time has been to "lock away" carbon.  They remove carbon dioxide during photosynthesis:

These carbohydrates have been used to:

1. Make more biomass (plant mass or growth)
2. Enrich the soil with organic matter
3. Removed carbon long term and be stored as coal underground.

In addition, carbon dioxide is removed when it dissolves on sea water.  It is combined with calcium by many mollusks and corals to make calcium carbonate or limestone.  

When the reef is buried or compressed the process of limestone formation is complete.  This kind of removal is another long term storage way of storing carbon and keeping locked out of the atmosphere.

It is fortunate that we have this means of removing carbon (especially carbon dioxide) out of the atmosphere and storing long term (i.e. 10's or 100's of millions of years). It is this reason that the planet has had a stable climate for so long.  If this hadn't happened Earth may have shared the same fate as Venus with a runaway greenhouse effect and surface temperatures over  400 Celcius.

Earth's Atmosphere over time.

The Earth's early atmosphere would have consisted of light volatile (low boiling point) gases contained in the meteorites and other bodies that were colliding with Earth.  These would have escaped into space.  Gases such as hydrogen and helium, bromine and iodine would have been lost very early on. 

As the crust formed on the earth and began to stabilise (around 3.8 billion years ago), volcanoes would have been the major contributor of the atmosphere.  This process is called outgassing.  Analysis of volcanoes today give us a clue to what may have been in the Earths "2nd atmosphere".  One point to note is the absence of oxygen. 

With the rise of the stromatolites and removal of iron from the oceans, oxygen began to accumulate in the atmosphere.  Since they began photosynthesis, the amount of CO2 also fell from the atmosphere.

The combine efforts of stromatoloites and the other photosynthetic organisms that followed lead to the composition of the atmosphere that we have today.  These levels are pretty typical of the planet for the last 450 million years.