L & B Visitors # 11 EarthCache
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Whilst visiting this very interesting and historical area I came upon these monolithic Black ice marble boulders that have been brought in from Chillagoe, Queensland (ancient sea site) so decided to do a bit of web searching to learn more about them.
It seems that marble is a metamorphic rock that is formed when limestone, a sedimentary rock composed mainly of skeletal fragments of marine organisms such as coral and molluscs, is subjected to heat and pressure in a metamorphism process. The mineral marble is composed of the mineral calcite (CaCO3). Marble is a white color in its purest form but does come in many nice shades depending on what mineral impurities it has in it. Marble may contain other minerals, such as clays, micas, quartz, pyrite, iron oxides, graphite, iron or manganese contamination . Under the high temperature and pressure conditions of metamorphism, the calcite in the limestone recrystallises to form a rock that is a mass of interlocking calcite crystals. Under these conditions the original limestone mineral is severely modified.
Marble is around 3 on the Mohs hardness scale, talc = 1, diamond = 10. At this hardness the stone is easy to cut to any needed shapes and sizes or ground up for other uses. These boulders located here have been cut to form a flat smooth surface on one side but the other side show weathering by mother nature.
My questions for you are: Please send your answers to these simple tasks to the cache owner by message or email.
1. Do you see any fossilised shells or coral in the black marble's polished surface? Please give a reason to explain your answer.
2. What additional mineral do you think has caused the black color?
3. Describe the texture of the weathering? Please check the natural side of the boulders. Are there any changes in colour?
Thank you for visiting this earth cache and hope that you enjoy you visit to the area.
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