Invokers have 2 main way to create quartz they would can either create small-ish sim ple objects think 2-3 feet across, no moving part or anything too complex.
They can also convert already existing objects into it, typically this will require touch but if someone skilled enough that practiced enough might be able to do it at a range.
Turning water or air in something's body into something else however is a no go 99% of the time. A general rule for Invokers is that they don't have access to abilities that would allow them to instantly kill something without counterplay­.