Compositional trends in rock-forming elements of comet Halley dust.
The VEGA 1 and 2 spacecraft flew by comet P/Halley in 1986 carrying, among other instruments, two mass spectrometers to measure the elemental composition of dust particles emitted from the comet.  Most particles seem to be a mixture of silicates of variable magnesium-iron composition and organic matter.  Comprehensive study of data and consideration of the mass of dust particles reveal cometary grains of "unusual" composition:  magnesium-rich and iron-rich particles.  Magnesium-rich particles are most likely magnesium carbonates, which could not have formed under conditions of equilibrium condensation but rather require formation by aqueous alteration.  The composition of the iron-rich particles can also be related to secondary processes in the comet.
Fomenkova
M N
MN
Space Research Institute, Academy of Sciences, Moscow, Russia.
Kerridge
J F
JF
Marti
K
K
McFadden L-A
D004391:Dust / Q000032:analysis*; D007501:Iron / Q000032:analysis*; D008274:Magnesium / Q000032:analysis; D013058:Mass Spectrometry; D017640:Silicates / Q000032:analysis*; D016082:Solar System; D018531:Spacecraft / Q000295:instrumentation
D004391:Dust; D017640:Silicates; C005479:magnesium carbonate; D007501:Iron; D008274:Magnesium