Study Set Content:
Can be defined as the degree to which a mineral grain or grains appear to stand out from the mounting mineral
RELIEF
• Can be defined as the degree to which a mineral grain or grains appear to stand out from the mounting mineral, whether it is
immersion oil, Canada Balsam other medium, or another mineral.
A mineral may exhibit () relief:
positive or negative
ndex of refraction for the material, is greater than the index of the oil
A +ve relief
A +ve relief E.g
garnet 1.76
nmin
A –ve relief
A –ve relief E.g.
fluorite 1.433
Garnet
1.72-1.89
Fluorite
1.434
Apatite
1.63-1.66
Orthoclase
1.51-1.52
quartz
1.54
Beryl
1.56-1.60
R1 Mounting Medium =
1.54
R1 medium =
R1 quartz
To determine whether a mineral has positive or negative relief, the() method is used.
Becke line
are a band or rim of light visible along the grain boundary in plane light when the grain mount is slightly out of focus.
Becke Lines
It may lie inside or outside the mineral grain depending on how the microscope is
focused
They are interpreted to be produced as a result of
1. the lens effect and/ or 2. internal reflection effect
when the refractive index of the mineral is greater than that of the immersion medium, a white line (becke line) () the fragments and moves into the fragments as the focus is raised
Forms around
