Some press conference results:
1. Ph is *buffered* to 8.3, same as sea water on Earth.
2. Calcium carbonate at 7% or more confirmed by both TEGA and MECA.
3. Phyllosilicate clays also abundant.
4. Extreme dryness of soil might be related to perchlorate prevalence.
5. So far "not able to claim organics" but apparently some weak or ambiguous signal for such. Not a lot of organic material, if present.