It's not a crystal anymore, it's a gear.Crystal — click wooden plus (bottom left) — Click your current profile (probably coal) — click the name tag.
Sadly you can only invite people on a coop and not a solo (it says what it is on the right hand side under the coins).
It is still a crystal on java I believe.It's not a crystal anymore, it's a gear.
okIt is still a crystal on java I believe.