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 is a valuable mineral that starts with the letter "O." It is known for its unique play of colors and is often used in jewelry.
Orthoclase
Zircon is a mineral that starts with the letter "Z". It is a silicate mineral commonly used in jewelry as a gemstone.
Aluminum is a mineral. It begins with the letter A.
Do you mean what Norse god starts with o? Odin is a Norse go that starts with O.
Emerald
Feldspar
Jade
mineral
mineral
igneous