In the lytic phase, the virus starts to replicate, so its DNA gets transcribed and translated by cellular enzymes, in order to form viral proteins, which are packaged into new viruses.
He had thought then that it was another order form for Weasleys'Wizard Wheezes, but it didn't look like that this time; if it had been, they would surely have let Lee Jordan in on the joke.
The crystals need lava-like temperatures in order to form, so it is likely that they formed near the surface of the forming star, were carried out to the surrounding gas cloud, and fell back down like glitter.