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THE INFLUENCE OF GEOLOGIC SAMPLE SURFACES ON THERMAL INFRARED REFLECTANCE SPECTROSCOPY
EVELIEN ROST, CHRIS HECKER, FREEK VAN DER MEER
MARTIN SCHODLOK, BGR
LABORATORY TIR SPECTROSCOPY
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℗ Mineral Fractions
Feldspar 50%
Pyroxene 30%
Quartz 20%
Spectral unmixing
TIR spectra influenced by e.g.:
Surface roughness
Crystallographic orientation
Grain size
Packing density
ROCK SAMPLESGildehaus SStFontainebleau SSt Shanxi gabbro
Fine grained
100% Quartz
6% porosity
Medium grained
99% Quartz
1% Kaolinite
~20% porosity
Fine grained
57% Feldspar
28% Pyroxene
Intergranular
6% Quartz,
6% Hornblende
1% Biotite, 1% Epidote,
0.5% Ilmenite
SAMPLE PREPARATION
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Sample surface preparations
Differences in surface roughness:
Split, Saw, Polish (grit of 4000)
Washed, compressed air, oven dried @ 50°C for ~8h
Cooling in desiccator for ~12h
METHODS – SPECTRAL MEASUREMENTS
Point measurements
Bruker Vertex70 FTIR with DHR integrating sphere
Studied range 7.5 – 16 µm
Spectral resolution 4 cm-1
9 measurements/sample surface
℗Symbol
METHODS – SPECTRAL MEASUREMENTS
TIR images
SPECIM AisaOWL LWIR hyperspectral sensor
Spectral range 7.7 – 12.5 µm
Spectral resolution 100 nm
▒Symbol
Surface roughness scans with Bruker
contour GT-I profilometer
METHODS – SAMPLE SURFACE ANALYSIS
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Scanning electron microscopy (SEM)
METHODS – DATA PROCESSING
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℗
▒
QX
RD
EnM
AP
Box: IS
MA
Mineral Fractions
Feldspar 50%
Pyroxene 30%
Quartz 20%
CSIRO Speclib Sample Speclib
Input for spectral unmixing
Surface
roughness
Unmixed minerals
Mean StdDev
Polished Quartz
Kaol
99.9%
0.01%
± 0.30
± 0.01
Sawed Quartz 100% ± 0.50
Split Quartz 100% ± 0.49
RESULTS – GILDEHAUS
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Point measurements ℗ LWIR images ▒
Surface
roughness
Unmixed minerals
Mean StdDev
Polished Quartz 100% ± 0.25
Sawed Quartz 100% ± 0.33
Split Quartz 100% ± 0.50
Up to 50% kaol for
individual pixelsOnly kaolinite unmixed for polished surface,
also observed with biotite in gabbro
DISCUSSION
Gildehaus: How can we explain these differences?
Observations confirmed by SEM images
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Polished zoom-in
Kaol
Qrtz
Kaol
Polished zoom-in20 𝝁𝒎
Qrtz
10 𝝁𝒎
Polished
DISCUSSION
11
Sawed
Polished
Ra 20,5
Rq 22,9
Rp 51,5
Rv -113,2
Rt 164,7
Sawed
Ra 11,2
Rq 17,1
Rp 93,3
Rv -103,4
Rt 196,7
arithmetic average roughness Ra
rootmean squared roughness Rq
maximum peak height Rp
maximum valley depth Rv
maximum height of profile Rt
Polished
Ra 20,5
Rq 22,9
Rp 51,5
Rv -113,2
Rt 164,7
Sawed
Ra 11,2
Rq 17,1
Rp 93,3
Rv -103,4
Rt 196,7
arithmetic average roughness Ra
rootmean squared roughness Rq
maximum peak height Rp
maximum valley depth Rv
maximum height of profile Rt
Polished
Ra 20,5
Rq 22,9
Rp 51,5
Rv -113,2
Rt 164,7
Sawed
Ra 11,2
Rq 17,1
Rp 93,3
Rv -103,4
Rt 196,7
arithmetic average roughness Ra
rootmean squared roughness Rq
maximum peak height Rp
maximum valley depth Rv
maximum height of profile Rt
Gildehaus: How can we explain these differences?
DISCUSSION
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Quartz
Kaolinite
Polish
Sawed Polished
THE INFLUENCE OF GEOLOGIC SAMPLE SURFACES ON TIR SPECTROSCOPY
EVELIEN ROST, CHRIS HECKER, FREEK VAN DER MEER
MARTIN SCHODLOK, BGR
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