This is Tillandsia Capitata, a species that can look amazing in a desert-style terrarium. They do not require compost and can also be fixed to structures such as driftwood, shells or even picture frames.
These curious plants absorb moisture from the air and especially enjoy medium humidity levels.
This particular variety is a desert-type of air plant that likes high light levels.
Fairly drought-tolerant as they have thick, silvery-green leves.
The leaves can turn a pinky-colour near to flowering time.
Require spraying with a little water regularly, or can be soaked, preferably in rain water, for short periods of time.
There is also an air-plant spray that is sometimes available - this provides additional nutrients.
Can produce exotic-looking flowers if growing conditions are correct.