Hornblende
Amphiboles; Double-chain Silicates
Monoclinic (-,+)
Relief - moderate
Colour - green or brown (oxy-hornblende)
RI - 1.61-1.76
Birefringence - 0.02
Interference colours - 2nd-3rd order, masked by the body colour
Extinction - inclined, complete
Comments - simple twinning is common
perfect cleavage in hornblende
PPL
Fish Canyon Tuff
simple twin in hornblende
PPL
Fish Canyon Tuff
basal section of hornblende, showing the two cleavages intersecting at 120°/60°
PPL
Fish Canyon Tuff
Euhedral, acicular hornblende
PPL
vosgesite, Assynt
Euhedral, acicular hornblende
XPL
vosgesite, Assynt
euhedral crystal of hornblende showing pleochroism as the crystal is roataed through 90°. This crystal also shows concentric zoning.
PPL
Fish Canyon Tuff
Euhedral rhombic and acicular crystals of hornblende; the basal section at the top left shows a simple twin.
PPL
vosgesite, Assynt
simple twinned crystal of hornblende
PPL
Fish Canyon Tuff