A – denotes accessory minerals. Colours under the microscope should be noted both under PPL and XPL.
Extinction angle and Interference Colours (Birofingence) is always observed under XPL. Some minerals such as dolomite verses calcite are difficult to identify without a hand sample. These images are NOT a replacement for hands on lab experience. If you find any errors, please contact me.
Microscope: Nikon H550S Camera: Samsung 8 MP, 3264×2448 pixels Date(s): 29-March-2013 to 12-April-2013 Samples: Epoxy has an R.I. of 1.55 +/‐ 0.01; thin sections varies between xx-xx μm Image Size: 1500 x 1500 pix File Name: Mineral name, Type of polarity and Thin section number (if more than one image, the file number); For example; min_kyanite_xpl_CK192_2.jpg.
While every effort is made to ensure that the content of this website is accurate, the data is provided “as is” and is not intended to be used as a primary reference material. While the lab samples are provided by the University of Calgary, the images on this site are sole property of Sanuja Senanayake. There is no affiliation between the University and sanuja.com. The the accuracy of data is not verified by any entity.
Colour balance issues; since it was extremely hard to calibrate the digital camera to reflect the true colours and due to various other factors, the colours in these images may not be perfectly accurate. For example, the Calcite in PPL suppose to look clear.
I recently came across a textbook, Basic Geological Mapping1, which is written for novice users. I found few interesting things in the introduction chapter that one might argue “kind of odd” for a well-written Continue reading Odd advice for a Field Geologist→
As a student, I am fascinated with economically important ore minerals such as diamonds. If we look beyond the jewelry aspect, diamonds are used in variety of applications. Diamonds are made of pure native carbons. Pure carbon can exist as a mineral in two different variations in Continue reading Diamonds beyond jewelry→
The following images are taken from a Samsung S III phone (Yes, you can’t believe the quality of detail on these images came from a 8 pix camera; contact me for technical/electronics detail on that) during the lab periods for Geology 311 (Mineralogy and Rocks) Winter 2013 at the University of Calgary.
Please click on the image on the left to access the larger original file. Download the PDF Version here.
Igneous and Precipitate Minerals and Rocks
Chem: K(Fe,Mg)3AlSi3O10(OH)2 Type: Sheet / Phyllosiclicate Structure: T-O-T+c structure Comp. Anio: (Si4O10)4- Si-to-O: 2 ; 5 Cry. sys: Monoclinic Hd: 2.5 / 3.0 Hs: shiny black Col/pleo: tan/straw brown – dark brown or green – brown green Relief: moderate/+ve Cleve: perfect cleavage Twin: none Habit: massive/platy Ext: parallel / pebbly Int. col: 3rd – 4th Other: vitrous
Chem: CaCO3 Type: rhombohedral / trigonal Hd: 3 Hs: Colourless, white, grey colourless, maybe dirty Relief: high/positive Cleve: brittle / concoidal black with pastel stripes Twin: wiggly twins?!? Habit: crystalline/granular Ext: twinkling extinction Int. Col: VERY HIGH – 4th order Other: reacts readily with HCl
Chem: FeCr2O4 Hs: brown streak, metallic luster, black granular Other: black under both xpl and ppl
(Ca,Fe,Mg,Mn)3Al2Si3O12 Orthosilicate / Nesosilicate T-O structure Comp. An: SiO44- Si-to-O: 1 ; 4 Type: isometric / cubic Hd: 6.5 – 7 Hs: red but variety too Col/pleo: clear/dirty – none Relief: high/positive Twin: none/uneven Habit: blocky/cubic Ext: NA
Chem: Ca2(Mg,Fe)5Si8O22(OH)2 Inosilicate Monoclinic moderate/+ve green under PPL
Chem: Al2SiO5 Orthosilicate / Nesosilicate orthorhombic 7-7.5 red? Dark cross-like in x-section = chiasolite Col/pleo: clear/dirty – darker than Cordierite in ppl Relief: moderate/+ve Ext: parallel Int. Col: 1st – grey Other: looks like a dirtier Cordierite, higher relief LOW PRESSURE POLYMORPH
Bedding vs Cleavage
To be updated…
This rock is formed deep underground about ~15 to 30 km of depth with between ~200 to 500 degrees Celsius. Blue colour is caused by Glaucophane mineral in the rock, which is a type of amphibole.
Chem: SiO2 Hd: 7 Hs: black, grey, white Col/pleo: dirty brownish grains – none Relief: low/-ve Cleve: none/concoidal Habit: nodules Int. col: 1st – grey/white Notes: not a true mineral rather a siliceous ooze – fine crystalline in xpl. Hardness same as quartz
Chalcedony and cavity filled with quartz
Chalcedony is a type of fibrous cryptocrystalline to fine grained silica that forms in pores, cavities and vugs in pre-existing rocks by precipitation from Si-rich fluids that pass through the rocks. Agate is a more brightly coloured variety of chalcedony that typically shows colour banding, with the colours being due to trace amounts of iron and manganese (or, increasingly, to dyes!). The concentrically banded geodes that you see in rock shops are vugs that have been partially to wholly filled with chalcedony/agate.
Chem: (Mg,Fe)3(Si,Al)4O10(OH)2*(Mg,Fe)3(OH)6 Sheet / Phyllosillicate T-O-T structure Monoclinic Hd: 2-2.5 Hs: green clear – green Relief: high/positive Cleve: perfect cleavage foliated masses – 2nd – Berlin Blue Other: has inclusions
To be updated…
CaMg(CO3)2 rhombohedral / trigonal Hd: 3.5 – 4 Hs: Colourless, white, grey (due to impurities, it can be many colours) Col/pleo: colourless/none Relief: low-moderate Cleve: perfect Twin: black with pastel stripes, wiggly twins?!? Habit: crystalline/granular Ext: twinkling extinction Int. Col: VERY HIGH – 4th order Other: Sugary texture may only be observed in finely crystalline dolomite as opposed to curved crystals faces of coarse dolomite. HCL reaction is very poor to none. It is extremely difficult to separate dolomite from calcite using a thin section. Precipitate mineral!
Chem: FeAl2O-OH[Si2O7][SiO4] Sorosilicate Monoclinic 6 silver/pistachio green yellow or green colourless to greenish yellow Relif: high/+ve brittle – planar lamellar (not common) fibrous, coarse to fine granular, massive. 3rd – bright green vitrous, Notes: pearly (Regional and contact metamorphic rocks)
Garnet with pressure shadows
Please check the information for the mineral in the igneous table above.
Hematite (Ore) (B), Quartz (A)
On the XPL photo, you can see the radiating cement of quartz (A) and the think black-brown (to dark reddish) outline of hematite (B) Hs: red-brown streak, steel gray and metallic shiny
Chem: Al2SiO5 Type: Triclinic Hd: 5.5-7 Hs: blue Col/pleo: clear Relief: high/+ve Twin: simple twins (sometimes) Habit: bladed / tabular Ext: inclined Int. Col: 1st – grey/yellow Other: HIGH PRESSURE POLYMORPH, may show stepped appearance like “tree-bark” in thinsection
Chem: (Fe,Mg,Zn)2Al9(Si,Al)4O20(OH)4 Type: Orthosilicate / Nesosilicate Monoclinic Hd: 7-7.5 Hs: dark brown / black Col/pleo: honey/potato yellow – none (ppl) Relief: high/+ve Cleve: subconcoidal Ext: zoning? Habit: intersecting prisms like a cross Int. Col: 2nd – mid/high yellow Other: poikiloblastic (air bubbles), “stauros” greek for cross – 2intersecting prisms HEXAGONAL SHAPED EUHEDRAL
Monoclinic 5.0-6.0 white, brown… colourless – none moderate/+ve brittle 2@60/120 silky, fibrous 2nd – bright turquoise similar to sillimanite in handsample
This type of rocks were originally limestone, now transformed into ‘Zebra’ dolomite.
At least partially fracture controlled, because of planar zones of coarse, light-coloured dolomite in darker, fine grained host. However, all of the rock now consists of dolomite, including the dark fine grained portions, suggesting an earlier period of pervasive dolomitization.
Halite and Gypsum
Halite is a Precipitate! Since it is white in colour, hand samples may be contaminated with other minerals causing it to appear in different coulours. The Halite is pretty much table salt, but do not taste it.
Gypsum has a sugary texture, curved crystal surfaces
Clinopyroxene Ca(Fe,Mg)Si2O6 Single Chain / Inosilcate T-O-T structure (SiO3)2- 1 ; 3 Monoclinic 5.0 – 7 shiny black – dull weathered black earthy/brown – nonpleochroic moderate/+ve 2@90 sometimes carlsbad / zoning thin lamellar tabular inclined (35-48) 2nd – low/mid
Apatite Ca5(PO4)3(F,Cl,OH) – – – – Hexagonal 5 very small usually – never see clear/none high/positive none/concoidal none six sided euhedral – 1st – grey/white usually a captured/ looks standing up… looks like quartz but really small
Tourmaline Na(Fe,Mg)3Al6(BO3)3(Si6O18)(OH)4 Ring / Cyclosilicate – Si6O1812- 1 ; 3 rhombohedral / trigonal 7 black hexagonal prisms seen in class? variable – variable moderate/+ve none none striated prism parallel 1st – 2nd – moderate
Cordierite Al2SiO5 Ring / Cyclosilicate orthorhombic 7-7.5 clear/dirty – lighter than Andalusite, has border moderate/+ve subconcoidal sector twinning 1st – grey/white looks like a cleaner andalusite, has patchy domains that extinct at different angles within crystal, has sometimes brown outlined border around crystal
Glaucophane Double Chain / Insolcate Monoclinic 5.0 – 6.0 grey/lavender blue lavender blue to striking blue (ppl) bladed / fibrous 3rd – bright blue
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