Zooming out from the patch:
NASA's Perseverance Mars Rover
On the plains of Jezero, the secrets of Mars' past await us! Follow for the latest news, updates, pretty pics, and community discussion on NASA and the Jet Propulsion Laboratory's most ambitious mission to Mars!
What are the purposes of this experiment?
We do these abrasions on the rocks before we start analyzing them in detail with the science instruments.
The geologists prefer not to analyze the raw, eroded outer surfaces of rocks - they tend to be covered in dust and sand, and they've been eaten away by the wind, or even (over long timescales) the minor amounts of humidity in the Martian atmosphere. By grinding away the outer surface, the fresh, unaltered interior of the rock is exposed.
The instruments then let you learn what minerals and other materials are in the rock, hopefully allowing us to ID what we're looking at. If the instruments turn up interesting results, the science team may decide to take a sample of the rock for eventual return to Earth.
Hope this helps. Feel free to ask if I wasn't clear about something.
Very cool. That makes sense, the outer surface may be some mixture of particles from many places but the interior would give a better indication of what the composition is deeper into the crust. Are there instruments capable of determine the age of the samples?
Not onboard the rover, no - which is one of the reasons many hardcore types are obsessed with sample return, in spite of the cost and extreme technical difficulty.
A number of age estimates for stuff in this area (the Jezero crater itself, the old mudstone down in the river delta we sampled last year, and so on) put them at easily 3.5 billion years plus - possibly older. That means the samples Perseverance already has in hand could be just as old as, or even older than, the most ancient sedimentary rock we've found on Earth. I get chills thinking about it.