Is Dormant Volcano legal in Standard, Modern, and Commander?

Dormant Volcano is legal in: Legacy, Vintage, Commander.

What type of card is Dormant Volcano?

Dormant Volcano is a Land. Its oracle text reads: "Dormant Volcano enters tapped.When Dormant Volcano enters, sacrifice it unless you return an untapped Mountain you control to its owner's hand.{T}: Add {C}{R}."

Dormant Volcano

Land

Dormant Volcano enters tapped.<br>When Dormant Volcano enters, sacrifice it unless you return an untapped Mountain you control to its owner's hand.<br>: Add .