Osmium is a mineral. It is a chemical element and has the symbol Os.
Calcium is one.
Marble.
A machine that starts with O is an oscillating fan.
talc topaz tourmaline
Oman is the only country that starts with O. There is no other country.
ore
Opal, (although it's not a true mineral).
Orthoclase
Aluminum is a mineral. It begins with the letter A.
Feldspar
Emerald
Zeolite.
Jade
mineral
mineral
Do you mean what Norse god starts with o? Odin is a Norse go that starts with O.
Andradite is a mineral and aplite is rock that start with the letter 'a'.