Frankly, I'm disappointed that the deposit turned out not to be a carbonate, but a sulfate.
On Earth of course there are both carbonate and sulfate deposits. So perhaps there are still extensive carbonate deposits on Mars.
In a prior post I said if there are no carbonates found here then the widely distributed white areas seen on Mars are probably due to sulfate, not carbonate. It MIGHT be that the white deposits seen at the Pathfinder site could still be carbonate. I was interested to see that at Meridiani, the wheels of the rover were able to grind up the white material located in the dug trenches. At Pathfinder, the Sojourner rover was unable to scratch the surface of the white material even with one of the spiked wheels meant to dig into the surface materials. It occurred to me that perhaps the Pathfinder white material was the harder caliche carbonate, while the Meridiani white material was the softer sulfate gypsum. Tony also raised the legitimate possibility the white material at Pathfinder is quartz. However, it maybe the difference in the two sites is simply that the MER rover is much heavier than the Sojourner rover and that is the reason it was able to grind up the white material.
But if the white areas seen on Mars really are all sulfate, we have a mystery. The (apparent) wide scale sulfate deposits suggest large scale water deposition. But if this is so and Mars once had a thicker CO2 atmosphere, there should also be large scale carbonate deposits. One possible explanation: some scientists argue that *large scale* carbonate deposits such as limestone require life to develop. Then perhaps the reason they are not seen on Mars is because life did not develop there.
Another possibility: perhaps when Mars had a thicker atmosphere (presumably it did to allow the large scale water deposition), that atmosphere did not consist of CO2. In addition to the lack of carbonate deposits seen on Mars we also have the mystery of the lack of CO2 in the Mars polar ice caps. Apparently, CO2 over the southern cap is only a thin covering:

Researchers Find Mars' South Pole Cap is Mostly Water Ice.
http://www.planetary.org/html/news/articlearchive/headlines/2003/mars_s-pole_water-ice.html

Perhaps that thicker atmosphere did not consist of CO2. Or perhaps as this article suggests the water cut channels seen on Mars occurred under an ice cover.
Or perhaps there are still carbonate deposits on Mars. One thing I would like to find out: are there some distinguishing factors surrounding sulfate deposits on Earth as compared to carbonate deposits? For instance do sulfate deposits occur most frequently near recent volcanic activity?

Bob Clark