The parish and town derive their names from the 'Kirk of the Muir'. The churchyard, has much history in it, and is worth a walk around. This is an EarthCache, and we are to look at the building blocks of the Kirk, the stone it is constructed from.
Colour plays an important part of our lives, it helps us to define and describe objects. It is the same with geology, and indeed can give us a hint about what it is made of.
Some examples of rock types and their colours:
Shales
These are typically composed of variable amounts of clay minerals and quartz grains and the typical color is gray. Addition of variable amounts of minor constituents alters the colour of the rock. Black shale results from the presence of greater than one percent carbonaceous material and indicates a reducing environment. Black shale can also be referred to as black metal. Red, brown and green colours are indicative of ferric oxide (hematite – reds), iron hydroxide (goethite – browns and limonite – yellow), or micaceous minerals (chlorite, biotite and illite – greens).
Sandstone
Colours will usually be tan or yellow (from a blend of the clear quartz with the dark amber feldspar content of the sand). The addition of Iron Oxide in some sands gives a reddish tint to the sand, while additional manganese gives a purplish hue. Red sandstones are also seen in the Southwest and West of Britain.
Limestone
Impurities (such as clay, sand, organic remains, iron oxide, and other materials) will cause limestones to exhibit different colors, especially with weathered surfaces. It is ordinarily white but may be colored by impurities, iron oxide making it brown, yellow, or red and carbon making it blue, black, or gray.
Granite
Granite consists of three main minerals: quartz and two kinds of feldspars (potassium and calcium-sodium) and mica. They form the structure of granite with equal amounts (30%). They all are colourless or white. And pyroxenes, amphibole or mica, being dark minerals, make 10%; they will be noticed in granite as separate scales or grains. When looked at from a distance, everything merges into grey colour. The more dark minerals has granite - the darker it is. The colour of some granite seems darker because of quartz which can be presented by morion.
Red granite. Bright red or pink feldspar are included into their mineral composition. The smallest crystals of hematite (oxide of iron) and red iron ore, disseminated regularly on all crystal of feldspar, give colouring to feldspar. Feldspar takes thick red colouring already when there is 0,7-1,0% of hematite in it. Granite feldspar acquires the pink colouring when maintenance of hematite does not exceed 0,3-0,4%.
Green granite. Such colour is given to granite due to inclusions of green potassium feldspar which is known for a long time as a semiprecious stone - amazon-stone (=amazonite the flying substances, accumulating in the central part of a vein, turned into amazone-stone (amazonite).
There are three main types of rocks:
Sedimentary, such as limestone, mudstone, sandstone.
Igneous, such as granite.
Metamorphic, such as slate and marble.
So why have I brought you here?
If you have read the above you will notice a common theme to most rocks, a mineral affects its colour.
This being an EarthCache, in order to log it, I ask that you answer some questions. Please send them to me, and do not include them in your log. You can send them to me by using the message facility or email, both of which can be found by looking at my profile. It is not meant to be difficult to do.
- How many colours can you see?
- What are the colours that you can see?
- What is the mineral reason for these colours?
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For full information on how you can expand the Church Micro series by sadexploration please read the Place your own Church Micro page before you contact him at churchmicro.co.uk
See also the Church Micro