emerald costs as much as a ruby and more than a diamond. One carat stone costs £20. The stones are cut brilliant, but the step form is more common. The dark stones are cut en cabochon and engraved. Aquamarine is also cut in pendant-shaped forms.
Synthetic spinel is often sold improperly as aquamarine. Doublets, triplets and glass imitations have also been made. Cut beryl and topaz look very much alike and may easily be mistaken for one another. But specific gravity, hardness and refractive index help to identify them correctly.
Formerly the name 'topaz' was very loosely used to denote a number of yellow stones. So yellow sapphire was known as 'oriental topaz', 'Scotch topaz', 'false topaz', and 'Madeira topaz'; smoky topaz for citrine and smoky quartz. Such use of terms leads to much confusion and should be entirely avoided. Real topaz ranks with beryl as a gem-stone.