From Pondok Layang Layang and towards Pondon Villosa - you will come across blocky steps of orange rock that have a pitted appearance. Where fresh they are green in colour, may have a 'soapy' feel, and can easily be scratched with a knife. These rocks are serpentinised peridotites, and were originally formed deep beneath the earth's ocean crust.
They were forced up from great depths during mountian building processess and then formed the basement on which sediments of the Crocker Formation were deposited.
Serpentinization
Serpentinization is a hydration and metamorphic transformation of ferromagnesian minerals, such as olivine and pyroxene, in mafic and ultramafic rock to produce serpentinite. Minerals formed by serpentinization include the serpentine group minerals (antigorite, lizardite, chrysotile), brucite, talc, Ni-Fe alloys, and magnetite. The mineral alteration is particularly important at the sea floor at tectonic plate boundaries.
Serpentinized rock such as the serpentinized peridotite seen on Mt Kinabalu happened as a by-product of peridotite - an dense, igneous ultramafic and coarse-grainedrock consisting mostly of silicate minerals such as olivine and pyroxene - reacting with sea water to form serpentinized peridotite.
In the Kinabalu area the most common peridotite is lherzolite, and tremolite-bearing peridotites whereas harzburgite and wehrlite are rare. lherzolite bearing peridotites are rich in olivine (40-90%) which is a magnesium iron silicate, while tremolite bering peridotites are rich in calcium, magnesium and iron.
How to claim this cache
Please study the write-up as well as conduct some independent research. Answer the following questions:
1. Describe how serpentinized peridotite is made.
2. Why does fresh serpentinized peridotite appear green?
Please refer to the geology poster present at Pondok Layang Layang. Please answer below:
3. The serpentinized peridotite on the trail is orange in colour. Please explain why this is the case.
4. Complete the sentence:
Serpentinite can easily become _________ and ________ so watch your _________ - especially when the trail is ______