Marble EarthCache

This Earth cache is not easy, but it's not a university course either. We have tried to explain things well enough so that anybody with a reasonable proficiency in English will be able to complete the cache, but it is quite detailed, so we have given it a difficulty rating of 4. We hope you will find out some interesting facts about marble, and see it being quarried, cut and used.

Allow at least one hour to visit all four waypoints, read the listing and answer the questions. You will need your own transport, preferably one that can handle a rough dirt road, though it doesn't need to be four-wheel-drive. Most of the cache can be done from beside your vehicle, though you will need to scramble up a steep bank for one waypoint. If you prefer not to drive or ride on the rough road, you can leave your vehicle by the sealed road at the turnoff waypoint, and walk the 1.5km to waypoints 1, 2 and 3, and back again. Either way, you will no doubt earn the terrain rating.

TO GET TO THE WAYPOINTS

You will be required to visit four waypoints to complete this Earth Cache. Waypoints 1, 2 and 3 are along the same dirt road that runs beside the expressway. While it might appear that these waypoints are actually on the E1 Expressway, they are not, and you WILL NOT be able to visit the waypoints from there. It is illegal and dangerous to stop on the expressway, and the things you need to see are not accessible from the highway.

If you are approaching from the Cameron Highlands, visit waypoint 4 first, then the other three. This waypoint is on the road from the Cameron Highlands. After visiting here, continue towards Ipoh and use the waypoint to find the turnoff for the dirt road. Follow the instructions below from the turn-off.

If you are approaching via the E1 Expressway, take the Simpang Pulai exit. After the toll gates, turn right, then take the next right at the traffic lights, towards Cameron Highlands. Use the waypoint given to find the turnoff for the dirt road.

From the turn-off, follow the dirt road between the walls and fences of the businesses there. You will soon reach Waypoint 1. Continue following this road to Waypoint 2, then Waypoint 3. Use the widening of the road to do a U-turn at Waypoint 3, though if you are enjoying exploring, you can continue on under the bridge, or on the same side of the road. Be warned that there might not be another turning point for a while. Maps do show that you can complete a circuit all the way back to waypoint 4, but access through the quarry site might be impossible, so we recommend that you return to the sealed road the same way you came, then turn towards Cameron Highlands to get to Waypoint 4.

THE FORMATION OF MARBLE

There are three main types of rock. Igneous rocks are formed when molten rock (magma) from below the Earth’s crust makes its way to the surface, or close enough to the surface that is cools and hardens. This is most often due to a volcanic eruption. Sedimentary rocks start as small particles that fall together to form a layer, which over time presses together to become rock. For example, mud and sand deposited at the bottom of rivers often become sedimentary rock. Metamorphic rocks occur when an igneous or sedimentary rock (or even another metamorphic rock!) is subjected to extreme heat or pressure, or chemically active fluids. The rock changes its structure and appearance, undergoing a metamorphosis, or change.

Marble is a metamorphic rock. It is usually metamorphosed limestone. Limestone is a very common sedimentary rock that is usually formed at the bottom of shallow oceans where the skeletons of ocean organisms (corals, forams, molluscs, etc) have fallen over many thousands of years. A layer of calcium carbonate (the remains of those skeletons) forms and hardens to become a rock, limestone. When limestone is subjected to extreme heat and/or pressure, usually deep within the Earth’s crust, it becomes marble. The heat or pressure causes changes in the geologic structure or minerals of the rock, and in the crystal structures (the crystals will change to a larger crystal type). Sometimes during metamorphosis, chemicals will leave or enter the rock, so the metamorphic rock may even be chemically different from its sedimentary relative.

Metamorphic rocks may be formed simply by the heat and pressure exerted on them because they are so deep underneath the surface of the Earth. Alternatively, they may have extreme pressure placed on them through tectonic forces, such as when two of the Earth’s major tectonic plates collide and push against each other. However, in the case of the Kinta Valley, it appears that the marble was formed when extreme heat was introduced by lava intrusions. That is, when molten rock from the Earth’s mantle forced its way over and through the limestone layers, super-heating all it came in contact with.

The change in particle size during metamorphism is called recrystallization. The small calcite crystals in limestone change during the metamorphism into much larger crystals. Both high temperatures and high pressure contribute to recrystallization. High temperature allows the atoms and ions in solid crystals to migrate, thus reorganising the crystals, while high pressures cause solution of the crystals within the rock, at the points of contact.

Metamorphic rocks, often formed deep beneath the Earth’s surface, eventually make their way to the surface through the processes of uplift (a section of rock is forced upwards) and erosion (material around the rock is washed or weathered away over time).

FOLIATION AND STYLOLITES

Foliation refers to the repetitive layering of a metamorphic rock. It occurs when parts of the rock are exposed to different pressures, causing what are essentially pressure lines in the rock. In a similar fashion, shearing forces placed on the rock also produce foliation. A different type of foliation can occur when the sedimentation layers are very different in compositions to each other, the foliation merely reflecting the differing mineral composition of the layers. Another type of foliation occurs when certain mineral flakes in the rock arrange their crystals in such a manner as to cause a layering effect. Foliation appears as regular, mostly parallel lines.

Stylolites are vein-like thready patterns that are common in marble. These may be caused by grains or layers that were in the limestone before metamorphism, or the result of selective erosion of veins in the limestone by water. The eroded veins fill with fine particles of silicates or other accessory minerals, usually creating a dark vein through the rock. After the rock metamorphises and becomes marble, these become the characteristic stylolites that appear as dark, wriggly and irregular lines in the marble.

IMPURITIES AND COLOURATION

Limestone (and therefore marble, as it is created from limestone) can contain a variety of impurities. These might include particles of other rocks, sand or mud, or other chemical compounds. These impurities can change the appearance and colour of the marble. For instance, the presence of iron oxide in marble often gives it a pink or red colouring. Silica or magnesium impurities can result in green colouring, and limonite can give the rock a yellow hue. If the limestone from which the marble was created is very pure calcium carbonate and contains few impurities, the marble will be pure white.

USES OF MARBLE

Pure white marble has long been prized for its use in sculpture. This is due to its relative softness (3 on Mohs scale) and resistance to shattering. Additionally, the refractive qualities of marble (the way that light bounces off and is absorbed by it), give carved marble a waxy appearance. Marble with no stylolites or foliation is easier to sculpt, as the result is more predictable.

Marble is also used widely in the building and furniture industry, as it is attractive when polished and wears well, except in the presence of acid rain (marble reacts to hydrochloric acid and is worn away by continual exposure to even weak acid). It has proved an attractive and strong building material. The largest producers of marble are Italy, China, Spain and India. While Malaysian marble is used locally and exported, dimension stone (granite and marble) accounts for a very small percentage of Malaysia's economy.

Marble is also used crushed, for applications such as road bases, and for industrial uses because it can neutralise acids.

MINING OF MARBLE

Marble shatters if not mined correctly. Blocks of marble are cut from the mountain with a channelling machine, which cuts grooves and holes in the rock. The block is outlined with rows of grooves and holes, then wedges are driven into the openings to separate the block from the surrounding rock. The cut block is taken to be cut by a machine, which cuts multiple parallel slices at the same time. This sliced rock is called dimension stone, and is used for bench-tops and tables, walls and floors.

QUESTIONS

Waypoint 1: Look carefully at the surface of the road. What do you see?

Waypoint 2: Pull over at GZ where the road is a little wider so other traffic can pass. Examine the marble next to you. Describe it in terms of:

• Size and shape
• Colour
• Foliation and/or stylolites
• Do you think it’s local marble from the Kinta Valley? Why or why not?
• Can you see any evidence of the mining process here?

Waypoint 3: Pull over where the road is a little wider. Climb up the embankment until you can see the marble mine (you don’t have to go all the way to the top- be safe!). You can see lines or layers across the mountain where the marble has been cut. How many layers high is the mine?

Waypoint 4: You can enter the car park of this business, Kintaly Marble and Granite. How many blades are on the cutting machine?

NOTE:We believe that the objective of an Earth Cache is to learn about geology whilst having fun in the outdoors. Finding "correct" answers is not as important as trying to understand the world around you. We encourage anybody to have a go and attempt this Earth Cache, and welcome all answers that have had some effort and thought put into them, whether they are "correct" or not. If you would like the answers sent to you, mention so in your email to the cache owner.

REFERENCES