The Dust was fully consumed. The flame is hotter than its size suggests, perhaps 2500 K. It lasted a fraction of a second. The energy seemed to come exclusively from the grain. The grain itself vanished completely (not sublimated) but the amount of energy released was less than the apparent mass of the grain times the speed of light squared. 

Background scans of Remnant's atmosphere do detect several exotic effects of varying magnitude. One of them exerts a sort of pressure on the Dust, as a heavy weight compresses a spring. "Triggering" the Dust involves supplying enough activation energy to overcome this pressure. 

"I think I know why dust doesn't work in space. If I'm right. It probably won't work at all off of Remnant." She explains about the way the magic she's detected works.

Do any of the other effects interact with dust?

No, just the one. 

Riley taps her staff twice and it splits apart with a single blank disk flying out before it fuses back together. She holds the disk in her hand as she crafts a new array to tune the coiling field in a limited radius. It takes her a minute or two to get it to work correctly. Then she sets another grain of fire dust into the test area. What happens if she reduces the strength of the coiling magic by 10%?

The grain explodes, just like the last one. 

Robyn watches and listens with interest, withholding comment for now. 

That was not the expected result. "Would it cause problems for me to fly to space from here? I want to see how the field drop off at the boundary."

"Uhhhhhh problems for you, maybe. Unless you can breathe in space. Which...you...probably...can." Robyn takes a moment to process this insight.

"Also I should clear it with traffic control." She opens her scroll to prepare. 

"That's what the helmet is for."

Robyn spends the next few minutes negotiating with a curt-voiced official over the scroll. 

There's plenty of grains of dust so Riley does another test. She adapts her array to make a gradient and levitates a grain slowly into the field.

It's not very far into the gradient before it spontaneously combusts. 5% reduction, approximately. 

Maybe a different type. Riley tries with air dust.

Same thing, but with a pop (and a whoosh of air) instead of flame. 

"Did your satellites explode when you tried to send them into space?"

"Pretty much. We tried with smaller samples first, and our electronics just fry themselves and go inert." Robyn returns her attention to listing security clearances. 

"I'm pretty sure I understand what's happening then. Still worth visiting space to confirm but that seems like about what's happening in my tests." For her next test she just leaves a grain of dust in a 4% reduction field for a while and watches to see if anything changes.

No spontaneous combustion occurs. 

And Robyn gets her cleared for spacegoing. 

"This shouldn't take long. Can you show me to the outside?"

Robyn leads the way, inquiring about Riley's tests thus far. 

Riley summarizes everything she'd found. Explaining the 5% threshold and how it seems equivalent to setting dust off in other ways. And then once they're outside she says "See you soon." And turns on a self-telekinesis array and rockets upward at just under the speed of sound. As she goes she scans the coiling field to see how it changes with altitude.

That'll give traffic control a headache, alright. 

The field is mostly stable until about 30 miles up at the upper edge of the stratosphere, at which point it drops off sharply. 

She hang about for a few moments to take a panoramic picture from that altitude and then lets herself fall restraining her maximum speed to just under mach one until she arrives back at Robyn's side.

It's one heck of a picture.