This form of opal is known as fire opal due to its colour - it can be red, orange or yellow. This specimen doesn't have flashes of colour so counts as "common opal", even though its colour is very intense. The pale cream coloured matrix accentuates the colour nicely. Most people think of flashy precious opal from Australia, but opal actually occurs in various colours and around the world. This specimen is discreetly glued to a white plastic base.
The final photo shows examples of all the different colours and forms of opal that I have on my web site (at least until some sell). Just put "opal" into the search box to see them all.
5/8 inch (1.6 cm) wide, 5/8 inch (1.6 cm) deep and 1/2 inch (1.3 cm) tall.