Parts of the microscope
Location of the cross polarizer on your microscope?
(Point to it!)
Where is the first polarizing filter the light passes through?
In the substage
How do you determine if a mineral is pleochroic?
Spin in PPL - if color changes it is pleochroic
How do you distinguish between Quartz and Plagioclase
Plag has polysynthetic twinning
Texture where crystals are uniformly large and interlocking
Phaneritic (intrusive)
How do you focus the ocular
Spin the one that is adjustable
How thick is a standard thin section?
30 um
How do you determine if a mineral has cleavage?
Look for faint parallel cracks. Usually most apparent in PPL
How do you distinguish biotite from hornblende
Habit and cleavage. Biotite has birds eye extinction.
Texture where crystals are uniformly tiny and interlocking
Aphanitic (volcanic)
Describe how to focus when using the highest power objective (40x)
FIRST, focus using the 4x, then again using the 10x, then finally using the 40x
If the light does NOT pass through a mineral between the upper and lower polarizers, what will you see in the microscope
Black - nothing
High relief vs. low relief - what do they look like?
High = bold dark grain edges and cracks
Low = faint grain edges and cracks
How do you distinguish Plagioclase from K-spar?
Plag has polysynthetic twinning, K-spar may have tartan or may have perthitic texture.
Texture where fragments of lithic and crystals are set in a matrix of ash (glass shards and dust)
Pyroclastic
What types of accessory plates do we have in the lab?
Mica (125 um) and gypsum (550 um)
If the light DOES pass through minerals, between the upper and lower polarizers, what will you see?
Interference colors
What is the birefringence of a mineral whose max interference color in the TS is 1st order orange
(look it up using chart)
How do you distinguish olivine from cpx?
Olivine has higher relief and higher interference colors.
Texture where larger crystals are set in a fine-grained crystalline groundmass
Porphyritic
Where is the bertrand lens?
(point to it!)
On a birefringence chart, show us where the 2nd order interference colors are.
(between the 1st and 2nd red dot on bottom of chart)
What is a mineral/material called when it is ALWAYS extinct in XPL?
Isotropic
How do you distinguish opx from cpx?
Opx has slight pleochroism, lower interference colors, parallel extinction
Texture where vesicles are filled with secondary minerals (i.e. minerals crystalized from groundwater AFTER formation of the igneous rock)
Amygdaloidal