Conversation so far:
What was the Spirit's main discovery?
The rocks are a type of basalt.
Which Martian rocks were analysed after the spirit rover mission was completed?
What materials do Martian rocks contain after the spirit rover mission was completed?
They contain the minerals olivine, pyroxene, plagioclase, and magnetite, and they look like volcanic basalt as they are fine-grained with irregular holes.
Where were the rocks found during the spirit rover mission?
The plains of Gusev
How did water alter the Martian rocks found during the spirit rover mission?
Outside coatings and cracks inside the rocks suggest water deposited minerals, maybe bromine compounds.
Did all the rocks found during the spirit rover missions contain water deposited minerals?
Are there any other interesting aspects about the Spirit (rover) article besides the rock analysis?
The dust in Gusev Crater is the same as dust all around the planet. All the dust was found to be magnetic.

Question: How did Spirit find out about magnetic dust?
Self-contained rewrite: How did Spirit find out about magnetic dust during the spirit rover mission?