The rocks on the plains of Gusev are a type of basalt.  They contain the minerals olivine, pyroxene, plagioclase, and magnetite, and they look like volcanic basalt as they are fine-grained with irregular holes (geologists would say they have vesicles and vugs).
Much of the soil on the plains came from the breakdown of the local rocks.  Fairly high levels of nickel were found in some soils; probably from meteorites.
Analysis shows that the rocks have been slightly altered by tiny amounts of water.  Outside coatings and cracks inside the rocks suggest water deposited minerals, maybe bromine compounds.  All the rocks contain a fine coating of dust and one or more harder rinds of material.  One type can be brushed off, while another needed to be ground off by the Rock Abrasion Tool (RAT).
There are a variety of rocks in the Columbia Hills (Mars), some of which have been altered by water, but not by very much water.
The dust in Gusev Crater is the same as dust all around the planet.  All the dust was found to be magnetic.  Moreover, Spirit found the magnetism was caused by the mineral magnetite, especially magnetite that contained the element titanium.  One magnet was able to completely divert all dust hence all Martian dust is thought to be magnetic.  The spectra of the dust was similar to spectra of bright, low thermal inertia regions like Tharsis and Arabia that have been detected by orbiting satellites.  A thin layer of dust, maybe less than one millimeter thick covers all surfaces.  Something in it contains a small amount of chemically bound water.