Saturday, 17 August 2013

The Chert of Pulau Saigon, a former island in the Singapore River

I must confess that I had not thought much about the chert of Southeast Asia until now. Is there a lot of chert in Southeast Asia? I don't really know firsthand. Most of the accessible beaches of Singapore are artificial and made of recent sand depositions from other places, and there are no points at which I can simply casually wade in and around the gravel of the Singapore River - much unlike the Thames in London, which has many wide banks upon which one can wander about without disturbance. I have, on past occasions, observed the proliferation of chert in the River Thames, and also, the endless amounts of chert/flint on Lyme Bay. So, what sort of rock is to be found in the rivers of Southeast Asia then?


Chert/Flint with cute echinoid in Natural History Museum, London


Chert/Flint on River Thames (London, 2012)


Chert/Flint on Lyme Bay (Jurassic Coast, 2012)

To be honest, to this day I still feel that my definition of "chert" is a bit fuzzy, despite having several encounters with chert and having read up on chert before. I do know at very least that Chert is formed by the recrystallization of siliceous skeletons of marine animals into microcrystalline sedimentary rock. From what I have read so far on it, I'm going to just take it to be a more inclusive term for most of the microcrystalline quartz or silica. And as from what I saw and read at the Natural History Museum in London, flint refers to the chert commonly found in chalk or limestone...

From Wikipedia: "There is much confusion concerning the exact meanings and differences among the terms "chert", "chalcedony" and "flint" (as well as their numerous varieties). In petrology the term "chert" is used to refer generally to all rocks composed primarily of microcrystalline, cryptocrystalline and microfibrous quartz. The term does not include quartzite. Chalcedony is a microfibrous (microcrystaline with a fibrous structure) variety of quartz.

Strictly speaking, the term "flint" is reserved for varieties of chert which occur in chalk and marly limestone formations. Among non-geologists (in particular among archaeologists), the distinction between "flint" and "chert" is often one of quality - chert being lower quality than flint. This usage of the terminology is prevalent in America and is likely caused by early immigrants who imported the terms from England where most true flint (that found in chalk formations) was indeed of better quality than "common chert" (from limestone formations).

Among petrologists, chalcedony is sometimes considered separately from chert due to its fibrous structure. Since many cherts contain both microcrystaline and microfibrous quartz, it is sometimes difficult to classify a rock as completely chalcedony, thus its general inclusion as a variety of chert."

I am fed up with local people having the name "Chert", thus foiling my attempts to investigate whether Chert rock naturally occurs in this region. Anyway, the reason why I am wondering whether there is a lot of chert in the Singapore River is because of this chert specimen in the Singapore River. Knowing that some of the slate comes from the UK, I realised I had never seen THE CHERT OF SINGAPORE in person before, although I have many Chert specimens from the UK, so I wondered if this chert rock had actually come from elsewhere....



Chert rescued from Pulau Saigon, a former island in the Singapore River

How do we tell this is "chert"? Largely because of its "waxy luster" and conchoidal fractures, which produce a sharp edge. Brittle materials such as chert have this quality, allowing it to be shaped into knives and tools.



Conchoidal fractures



Waxy Luster

Today I was very fortunate to be able to spend a few hours at the Archaeology Lab at NUS, where I attempted to do a preliminary photoshoot of certain artefacts from Pulau Saigon, and began running some shots through Autodesk's 123d Catch in order to produce 3d models of some of the objects. Thank you to John Miksic and Goh Geok Yian for letting me occupy their pantry for the entire day and sharing with me about their work. It will take me some time to process all the information captured today, but you can expect more posts on the topic in coming weeks... (They always need more committed and responsible volunteers at their lab to help them sift through, sort through, and wash material, so if you're interested in archaeology in Singapore and are available to volunteer your time on Fridays between 10-5pm, leave me a note and I will pass your contact on to them.)


Pulau Saigon (PSG) Stone and Rocks






14th C Stoneware


European Porcelain

Oh and another strange thing that happened is that I encountered the word "Diatomaceous" twice within one hour today. Whilst reading the comments to an instructable about building a solar food dryer to find out if others were worried about insects getting into their solar food dryer, I discovered a comment suggesting that "Diatomaceous earth" be scattered because its tiny, light yet highly abrasive nature makes it suitable as a mechanical insecticide, making it unpleasant for tiny ants to walk upon - basically getting inbetween their tiny exoskeleton joints and absorbing lipids from the waxy outer layer of insects' exoskeletons, causing them to dehydrate from the inside out rather quickly, leading to the death of the insects. A few minutes later I read that chert occurs in diatomaceous deposits and that kind of chert is known as diatomaceous chert. The word diatomaceous refers to diatoms, which consist of tiny microscopic marine phytoplankton, along with their fossils...

Which brings me to.... MICROPALEONTOLOGY, and the study of microfossils! Anything that you can study with the naked eye is probably considered a macrofossil. Micropaleontology is surely a field of study that is after my heart. A micropaleontologist might typically be a specialists in one or more taxonomic groups because it is something that requires so much specialisation to study the fossils of tiny tiny creatures. Speaking of tiny things, this reminds me of micrometeorites. And subsequently... astrogeology. I think this week if you asked me what is my dream job might be, it might be to study to become a micropaleontologist or an astrogeologist. Yeah, I can dream, can't I?

See also:

The Mineral collection at the Natural History Museum, and Flint Nodules along the River Thames
Bone, Metal, Wood, and Other Artefacts found on Pulau Saigon
Made-up Road Names and Temporary Islands
Ruins in Reverse

1 comment:

  1. There's a nice podcast about that:

    And the exact manner in which chert/flint concretions grow in the surrounding (chalk) layers is still not completely understood (read this in a small geology booklet).