Mirror Lake, locally known as Tasik Cermin, is a hidden lake enclosed by limestone karst formations of Gunung Rapat. It is a rare gem that cannot be found on any tourist maps and the type of location you typically stumble upon while accidentally reading someone's blog, or via word of mouth.
The tunnel leading to and fro Mirror Lake (Tasik Cermin).
(Source: Barnyard Dawg, 2018)
Type of EarthCache: Mineralogy / Mineral deposition.
Gunung Rapat
Gunung Rapat is one of 45 limestone hills found in Perak's Kinta Valley. It is part of the Calcareous Series that formed limestone hills consisting almost entirely of crystalline (composed of crystals) limestone, which is lacking in fossils and assumed to be of Permian age (440 to 280 million years ago).
Calcite / Calcium Carbonate
Calcite is a very common carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). The mineral appears in a very wide variety and its hexagonal ditrigonal scalenohedral class contains over 800 identified forms and well over 1000 combinations.
With a hardness of 3, calcite resides at the lower end of Mohs scale of mineral hardness, alongside gypsum and fluorite. Mohs scale of mineral hardness measures scratch resistance of various minerals through the ability of harder material to scratch softer material. While calcite scratches easily and readily dissolves in dilute acid, diamond would find itself on the highest end of Mohs scale.
Calcite is also a cousin to aragonite which forms the shells of many clams and brachiopods. Calcite has more forms and habits than any other mineral and add to that a wide spectrum of colours from clear to black. But the streak is always white or a pale color.
The main calcite deposit.
(Source: Barnyard Dawg, 2018)
The process of calcite deposition
In limestone caves, or in this case a manmade tunnel dug mid-20th century, after the natural process of erosion and excavation, a simple but slow natural process is responsible for the decoration of the bare, dull walls.
Falling rain picks up atmospheric carbon dioxide. On passing through the soil, more carbon dioxide, from plant roots and decaying vegetable matter, becomes dissolved in the water, along with complex organic acids called humic acids ((HAs). This slightly acidic ground water easily dissolves limestone.
The solution slowly descends into the cave and deposits the dissolved calcium carbonate, sometimes including impurities of iron and other minerals. On reaching the cave, the water droplets fall to the floor or trickle down a rockface, leaving behind a tiny deposit of calcite crystal. Early-forming calcite has relatively good crystal form because of the large growth space available. Late-forming calcite has poor crystal form because of limited growth space.
Given time, these calcite crystal deposits will eventually result in speleothems.
Speleothems
There are four major types of speleothems; dripstones, flowstones, pore deposits and pool deposits.
1. Dripstones:
- a) Straws - Straws are thin walled hollow formations that resemble drinking straws. As water drips slowly from the roof of the cave, it deposits a microscopic ring of calcite crystal. These rings continue to build and can form straws many centimetres long.
- b) Stalactites - Stalactites are formations that grow downwards from the cave roof. Nearly all stalactites start as a straw. When the straw becomes blocked with calcite or impurities, a stalactite starts to develop and thicken over the years, from the solution which runs down its outer surface.
- c) Stalagmites - Stalagmites are solid dripstones that grow upwards from the cave floor, from each drop of water from the roof or from stalactites overhead.
- d) Columns or Pillars - Columns or Pillars are formations that develop from stalactites or stalagmites that extend from floor to roof.
2. Flowstones:
- a) Shawls - Water reaching the roof of a cave does not always form drops. Sometimes it trickles down a rockface, depositing a narrow strip of calcite, that eventually results in a thin sheet, growing at an angle from the wall. Shawls often contain interesting folds, which occur because the initial trickle turned from side to side in its downward path along the rockface. The rich coloured banding that is often seen, is caused by other minerals in the solution, such as iron oxide.
- b) Flowstones - These attractive formations occur when flowing water leaves a film of calcite. They cover the original rock or mud floor, often to a considerable thickness. Sometimes the lower portions hang free, making a fringe or shawl of stalactites.
3. Pore Deposits:
- a) Helictites - Helictites are formed by water slowly entering the caves through pores and cracks in the limestone. Helictites are named from the Greek word 'helix', meaning 'a twist'. They are small irregular growths which proceed in any direction contrary to gravity. The most accepted theory for their growth and development is a combination of capillary action and hydrostatic pressure. The saturated solution emanates from a pore so slowly that it doesn't form a drop. Evaporation occurs and a minute layer of crystal is deposited. A capillary tube slowly develops, through which the solution is drawn, extending the helictite. Because no drop forms, gravity has no effect and the helictite can develop in any direction, defying gravity.
- b) Cave Corals - Subaerial cave corals are another form of pore deposit that develops as the solution seeps from cave walls, depositing layers of calcite crystal. Capillary tubes do not form, and the growth can develop over large areas. They have a rough texture and may resemble cauliflower.
4. Pool Deposits:
- a) Rimstone - Rimstone dams or gours are fragile vertical walls that build up as cave pools overflow, depositing calcite at the edges. At the point of overflow, calcite is precipitated as CO² loss occurs.
- b) Dogtooth Spar - Dogtooth Spar is a pool deposit that forms under extremely still conditions, where there is little or no water movement. This allows the the supersaturated solution to form large crystal faces and perfect form. Dogtooth Spar also forms in vugs (mineral lined rock cavities) which are later exposed as the cave develops.
- c) Cave Pearls - Cave Pearls are spherical and develop in saturated pools. The calcite forms around a nucleus, such as a tiny pebble or grain of sand. Calcite crystal builds up as the pearls are agitated, usually through drops of water from the cave surroundings.
- d) Lily Pads or Shelfstone - Lily Pads or Shelfstone form around the edges of cave pools or existing dripstone formations, such as stalactites, stalagmites and columns. They usually develop under still water conditions and a constant pool level.
How to claim this EarthCache?
Coordinates are hard to fix inside a tunnel. When walking in, you will find the calcite deposits on your right. Find the one nearest the exit. The calcite deposits can be easily identified; the crystals will reflect the light of your torch (or your phone's LED if need be), and appear to sparkle.
Send me the following;
1. The text "GC7RAGW Minex Quarry Tunnel - Calcite Deposition" on the first line.
2. The answers to the following questions;
- Going by the size of the deposition, are these early or late calcite deposits?
- Identify the main speleothem into which these calcite deposits are evolving.
- Identify the secondary speleothem evolving on the main speleothem.
- There are several larger calcite deposits in this tunnel, how many are there?
3. Provide a photo of yourself or a personal item to prove you have visited the site.*
References
* Effective immediately from 10 June 2019, photo requirements are permitted on EarthCaches. This task is not optional, it is an addition to existing logging tasks! Logs that do not meet all requirements posed will no longer be accepted.
For additional information, visit; Geosociety.org, Geocaching.com Help Center and Geocaching.com Forum.
Finding the answers to an EarthCache can often be challenging, and many people tend to shy away from these caches because of this. However, it is my opinion that geocaching is also meant to be a fun family experience that simply aims to introduce interesting and unique locations such as this one. Flexibility on logging requirements, however, can only be applied if it can be established that you have actually taken the time to visit the site. For this reason, a proper log describing your adventure accompanied by a good number of photos would be much appreciated.
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