It is not just the liquids which are to be carried in restricted quantities in airline cabin now. Added to the list are the powdery substances. Transportation Security Administration of the US has not explicitly banned the carriage of powdery substances in cabin baggage but has issued a strong directive that powdery substance of more than 350mL quantity (12 oz) need need to be carried in the check in baggage. This has come into force from June 30, 2019. 
TSA said that people carrying more than 350mL powdery substances would be subject to more screening and if they are not able to identify it, it will be confiscated. Further, it says that in the best interest of travelers and to avoid the hassles at airport, it is suggested to take the powdery substances of more than 350mL in check-in baggage.
While the directive was meant to be effective on all flights within the US and direct flights from international airports to US airports, the same is also being followed by all major airlines of the world. Governments and airlines worldwide have introduced ban on carriage of these substances in cabin if quantity is more than 350mL, roughly the size of a cola can.

Why this restriction?
The rationale for restriction on these substances is due to concerns of security. TSA believes that terrorists might use improvised powdery substances as explosives. It is also concerned about the effect of certain other common powders, such as pepper powder, if this is used in cabin on passengers. Hence, the need to place restrictions.

What type of powdery substances are to be banned?
TSA says that these substances could be protein powders, energy powder mixes, cosmetics, spices or other such items. While cremated human remains, baby formula and medicines are exempted, these do need prior declaration at the time of check in. 

How to define a powdery substance?
American Airlines has defined a powdery substance as fine dry particles produced by grinding, distintigration, crushing of a solid substance.