My theory is that Rose trapped both Lapis and Desert glass.
When we first saw the desert glass, it was building columns and stairs of sand. The gem is hostile towards the owner of the Rose Quartz/ Pink diamond gem. It tried to have Steven killed by Lion, but it failed because Lion has some affiliation with Rose. Lion even tried to save Steven from the Desert Glass at the very end. Lion also tagged along in Ocean gem, when Lapis was stealing the ocean. So far, the episodes with Lion reveal something big about Rose. I think the big thing about Rise in desert glass and mirror gem is that she trapped them inside.