©Lin Yangchen


Beneath the surface of a grey and dead-looking rock is a universe of colour, pattern and texture that comes alive under a polarizing microscope. Those who decode the information hidden within the Pink Panther-like tapestry of mineralcules gain access to the deepest secrets of the Earth and rule over the fashion catwalks of Paris and Milan.

I present here my analyses and photomicrographs of petrographic thin sections with my ‘Special Forces’ Olympus BHSP petrographic microscope. Reflected-light micrographs will be captioned as such. All other micrographs are in transmitted light. Mineral identifications are dependent on my progressive study of optical mineralogy and may not be error-free. Please contact me if you spot mistakes so I can correct them and make this a better reference for everyone. Also see my meteorite atlas and disco lighting videos.


Click individual samples:

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The author’s collection of geological and topographic maps of Singapore and Southeast Asia.


Accession no. R001

Locality: unknown (may not be Southeast Asia)
Sample date: unknown
Method: hand sample
Finder: unknown


Macroscopic description


Petrographic analysis

30 μm unpolished with no. 1 coverslip
Norland Optical Adhesive 61 (n = 1.56, US military specification MIL-A-3920)
prepared by Precision Petrographics, Canada


Malachite, hematite and isotropic garnet with golden veins.

Malachite.

Banded hematite.

Length-slow grain undergoing subtraction from low-second-order blue-green to mid-first-order white-yellow with 530 nm retardation plate. Quartz grain size ranges from microcrystalline to nearly 1 mm.



Accession no. R002

Locality: unknown (may not be Southeast Asia)
Sample date: unknown
Method: hand sample
Finder: unknown


Macroscopic description

Vesicular suevite impact melt breccia with hematite cement.
Embedded in Struers EpoFix (n = 1.578)


Unpolished
Reflected light cross-polarized

Petrographic analysis

30 μm unpolished with no. 1 coverslip
Norland Optical Adhesive 61 (n = 1.56, US military specification MIL-A-3920)
prepared by Precision Petrographics, Canada


Accession no. R003


The 1815 caldera of Tambora in September 2005.

Locality: western caldera rim of Tambora volcano, Sumbawa, Indonesia
Sample date: 23 September 2005
Method: hand sample
Finder: Lin Yangchen


Macroscopic description

Embedded in Struers EpoFix (n = 1.578)

Petrographic analysis

30 μm unpolished with no. 1 coverslip
Norland Optical Adhesive 61 (n = 1.56, US military specification MIL-A-3920)
prepared by Precision Petrographics, Canada
disco lighting video


Clinopyroxenes, olivine and opaque oxides in a matrix of plagioclase flakes and fine-grained groundmass.

Plagioclase hosting melt inclusions in earlier stages of crystal growth (see Nurfiani et al. 2021).

Combined oscillatory and sector zoning of clinopyroxene.
Slightly tilted acute bisectrix conoscopic Fourier transform interference figures of an unidentified biaxial grain of 2V > 45°. Tint plate not inserted. Numerical aperture 0.75.



Accession no. R004


The crater of Barujari in September 2005.

Locality: northeast foot of Barujari volcano in the Rinjani caldera, Lombok, Indonesia
Sample date: 18 September 2005
Method: hand sample
Finder: Lin Yangchen


Macroscopic description

Volcanic bomb of vesicular basalt.
Embedded in Struers EpoFix (n = 1.578)

Petrographic analysis

30 μm unpolished with no. 1 coverslip
Norland Optical Adhesive 61 (n = 1.56, US military specification MIL-A-3920)
prepared by Precision Petrographics, Canada


Plagioclase and clinopyroxenes in fine-grained groundmass with large irregular vesicles.


Microlite-rich groundmass with opaque magnetite grains.

Melt inclusions with bubbles in zoned plagioclase.


Accession no. R005

Locality: Bukit Gombak, Singapore
Sample date: 25 August 2021
Method: hand sample
Finder: Lin Yangchen


Macroscopic description


Petrographic analysis

30 μm unpolished with no. 1 coverslip
Norland Optical Adhesive 61 (n = 1.56, US military specification MIL-A-3920)
prepared by Precision Petrographics, Canada
Above quartz band.
Porphyry with phenocrysts of highly strained quartz and chloritized biotite.

Below quartz band.
Clinopyroxenes, heavily altered plagioclase, chloritized biotite, opaques.


The quartz band, with spectacular intergrowths of columnar muscovite (see Runyon et al. 2019).

  The rarely used configuration of parallel polarizers (top) reveals in a large quartz grain additional defects (yellow) and subparallel striations (purple) that are barely noticeable in cross-polarized light (lower left), even with stage rotation or a λ waveplate (lower right). Also see polychromatic polarization microscopy.

Conoscopic Fourier transform optic axis interference figures of a grain in the quartz band showing its uniaxial positive properties. Right, with 530 nm retardation plate. Numerical aperture 0.75.



Chloritized biotite with iron-rich regions yielding Berlin blue anomalous interference colour.

Kink bands in explosively deformed pleochroic reddish brown high-titanium biotite accompanied by quartz, clinopyroxene and opaques.


Euhedral zircon in chloritized biotite with pleochroic halo of radiation damage by uranium and thorium.


Accession no. R006

Locality: Bukit Gombak, Singapore
Sample date: 25 August 2021
Method: hand sample
Finder: Lin Yangchen


Macroscopic description
Leuco-granite dyke with fine-grained dolerite veins. Zircon U-Pb dated to Early Triassic, 249.9 ± 1.9 million years (Oliver et al. 2014).


Petrographic analysis

30 μm unpolished with no. 1 coverslip
Norland Optical Adhesive 61 (n = 1.56, US military specification MIL-A-3920)
prepared by Precision Petrographics, Canada


Porphyritic mosaic of undulose quartz and sericite flakes probably altered from plagioclase.

Close-up of vein showing pleochroic acicular mineral with zoned birefringence and straight extinction, possibly epidote.



Accession no. R007

Locality: Bukit Gombak, Singapore
Sample date: 25 August 2021
Method: hand sample
Finder: Lin Yangchen


Macroscopic description

Dolerite.

Petrographic analysis

30 μm unpolished with no. 1 coverslip
Norland Optical Adhesive 61 (n = 1.56, US military specification MIL-A-3920)
prepared by Precision Petrographics, Canada
Calcite veins dissecting fine dark groundmass with subparallel alignment of plagioclase laths and occasional larger grains of apatite, calcite, chlorite, clinopyroxene et al.


Calcite with extreme high-order birefringence and twinning visible in plane-polarized light.

Euhedral basal section of apatite.


Accession no. R008

Locality: Bukit Gombak, Singapore
Sample date: 25 August 2021
Method: hand sample
Finder: Lin Yangchen


Macroscopic description
Gombak Norite (a plutonic basic olivine gabbro). Coarse-grained equigranular bronzite (an orthopyroxene) and white plagioclase. Zircon U-Pb dated to Late Permian, 260.3 ± 2.3 million years (Oliver et al. 2014).


Petrographic analysis

30 μm unpolished with no. 1 coverslip
Norland Optical Adhesive 61 (n = 1.56, US military specification MIL-A-3920)
prepared by Precision Petrographics, Canada
disco lighting video

Plagioclase with polysynthetic twinning, exsolution lamellae and oscillatory zoning. Pyroxene with moderate relief and moderate interference colours. No pink-green pleochroism observed. Occasional opaques and fractured olivine with no cleavage. Oliver & Gupta (2017) recorded 50% calcic plagioclase, 35% orthopyroxene, 5% olivine, 5% brown hornblende and 5% opaques.

  Precise retardation measurement of a grain of plagioclase by means of de Sénarmont compensation in monochromatic illumination. An analyzer rotation of 100.3° was recorded, giving a retardation of 323 nm corresponding to a birefringence of about 0.011. Vignetting caused by the camera and the stopping down of the iris diaphragm to minimize oblique rays.



Pyroxenes with dark bands of alteration to coarse or fibrous amphibole.

Chagrined bronzite-augite lamellae with alternating straight and inclined extinction.

Augite twin with near-orthogonal cleavage planes and inclined extinction.

Hydrothermal sericitization of zoned plagioclase.

Sericitization bounded by the outline of what appears to have been a euhedral monoclinic phenocryst, possibly a clinopyroxene. The sericite exhibits localized fan-shaped structures with low relief and straight extinction. A rare occurrence in Gombak Norite (Lee & Zhou 2009).



Accession no. R009

Locality: Singapore, near Bukit Timah Fault
Sample date: 23 August 2021
Method: hand sample
Finder: Lin Yangchen


Macroscopic description
Weakly lithified fine-grained muddy marine sandstone of the Tengah Facies, Jurong Formation. Upper Triassic. Vacuum-impregnated with Burnham Petrographics Petropoxy 154 (n = 1.540 ± 0.001)


Unpolished
Reflected light cross-polarized

Petrographic analysis

30 μm unpolished with no. 1 coverslip
Norland Optical Adhesive 61 (n = 1.56, US military specification MIL-A-3920)
prepared by Precision Petrographics, Canada

Blend of quartz grains, opaque hematite and silt or clay aggregates with occasional minerals of higher birefringence.

Orange-red hematite cement. The morphology resembles that of sandstones of the Stormberg Group in South Africa (see Chima et al. 2018).


Hematite pellets surrounded by lightly chagrined quartz.



Mineralogy texts

Craig & Vaughan
Stephen Nelson
Dexter Perkins


Databases

Common minerals in thin section
Name That Mineral
Webmineral
Mindat


Petrographic atlases

University College London catalogue
Oxford Atlas of Metamorphic Minerals
NASA lunar samples
NOVA Mineralogy
Virtual Microscope
micROCKScopic
Kurt Hollocher
Alex Strekeisen
Dexter Perkins
Derochette
rockPTX
Rogers




References

[also see references within entries]
Bo, M. W., Arulrajah, A., Sukmak, P. & Horpibulsuk, S. 2015. Mineralogy and geotechnical properties of Singapore marine clay at Changi. Soils and Foundations 55(3):600–613.

Cai, J. G. 2012. Geology of Singapore. Tritech Consultants Pte Ltd.

Chima, P., Baiyegunhi, C., Liu, K. & Gwavava, O. 2018. Diagenesis and rock properties of sandstones from the Stormberg Group, Karoo Supergroup in the Eastern Cape Province of South Africa. Open Geosciences 10:740–771.

Cummings, D. 1965. Kink-bands: shock deformation of biotite resulting from a nuclear explosion. Science 148:950–952.

Geological Survey of Japan, Philippine Institute of Volcanology and Seismology & Volcanological Survey of Indonesia 2000. Report of International Research and Development Cooperation ITIT Projects: Research on Volcanic Hazard Assessment in Asia. International Research and Development Cooperation Division, Agency of Industrial Science and Technology, Ministry of International Trade and Industry, Tokyo, Japan.

Geotechnical Society of Singapore & Building and Construction Authority 2019. Guidelines on Identification of Rock During Bored Piling Works.

Gillespie, M. R., Kendall, R. S., Leslie, A. G., Millar, I. L., Dodd, T. J. H., Kearsey, T. I., Bide, T. P., Goodenough, K. M., Dobbs, M. R., Lee, M. K. W. & Chiam, K. 2019. The igneous rocks of Singapore: new insights to Palaeozoic and Mesozoic assembly of the Sukhothai Arc. Journal of Asian Earth Sciences.

Gorai, M. 1951. Petrological studies on plagioclase twins. American Mineralogist 36:884–901.

Kumarasamy, J. Singapore Geology and its Impact on Underground Construction Works.

Lee, K. W. & Zhou, Y. 2009. Geology of Singapore 2nd edition. Defence Science & Technology Agency, Singapore.

Nurfiani, D., Wang, X., Gunawan, H., Triastuty, H., Hidayat, D., Wei, S. J., Taisne, B. & de Maisonneuve, C. B. 2021. Combining petrology and seismology to unravel the plumbing system of a typical arc volcano: an example from Marapi, West Sumatra, Indonesia. Geochemistry, Geophysics, Geosystems 22:e2020GC009524.

Oliver, G. J. H. & Gupta, A. 2017. A Field Guide to the Geology of Singapore. Lee Kong Chian Natural History Museum, National University of Singapore.

Oliver, G. J. H., Khin Zaw, Hotson, M., Meffre, S. & Manka, T. 2014. U-Pb zircon geochronology of Early Permian to Late Triassic rocks from Singapore and Johor: a plate tectonic reinterpretation. Gondwana Research 26:132–143.

Public Works Department 1976. Geology of the Republic of Singapore.

Rachmat, H. & Iqbal, M. 2000. West Nusa Tenggara Volcanoes.

Raith, M. M., Raase, P. & Reinhardt, J. 2011. Guide to Thin Section Microscopy.

Runyon, S. E., Seedorff, E., Barton, M. D., Steele-MacInnis, M., Lecumberri-Sanchez, P. & Mazdab, F. K. 2019. Coarse muscovite veins and alteration in porphyry systems. Ore Geology Reviews 113:103045.

Scrivenor, J. B. 1924. The geology of Singapore island. With a geological sketch-map. Journal of the Malayan Branch of the Royal Asiatic Society 2(1):1–8.

Self, S., Rampino, M. R., Newton, M. S. & Wolff, J. A. 1984. Volcanological study of the great Tambora eruption of 1815. Geology 12:659–663.

Sharma, J. S., Chi, J. & Zhao, J. 1999. Geological and geotechnical features of Singapore: an overview. Tunnelling and Underground Space Technology 14(4):419–431.

Sigurdsson, H. & Carey, S. 1989. Plinian and co-ignimbrite tephra fall from the 1815 eruption of Tambora volcano. Bulletin of Volcanology 51:243–270.

Stothers, R. B. 1984. The great Tambora eruption in 1815 and its aftermath. Science 224:1191–1198.

Voort, G. F. V. 1999. Metallography: Principles and Practice. ASM International, USA.

Wong, P. P. 1969. The surface configuration of Singapore island: a quantitative description. The Journal of Tropical Geography 29:64–74.

Zhou, Y. & Zhao, J. 2016. Assessment and planning of underground space use in Singapore. Tunnelling and Underground Space Technology 55:249–256.