Genuine onyx is a mineral that is processed into gemstones. There is a confusion risk here mainly because different limestone-sintered stones are also summarised under this term. For jewellery production, of course, the mineral is interesting. Onyx is a variety of chalcedony, which is itself a variety of quartz. Onyx is therefore also a subspecies of quartz. Characteristic for onyx is its bicolouration of white and black, with the two colours alternating in layers in the mineral. These layers are very slightly translucent in onyx. Special forms, which are also called onyx, are chalcedones, which are exclusively black in colour. The name of the onyx is derived from the Greek and means something like claw or talon. Onyx jewellery is often worn on mourning occasions due to its black colouring, and onyx is particularly common in brooches. The mineral is also used in cufflinks, to be worn together with the big formal suit on special occasions. Onyx is often faked due to the high demand, whereby inferior agate is dyed or the colour of chalcedony is changed accordingly in an acid bath. The authenticity of onyxes can only be proven through close examination; only an occurrence of white colour in the gemstone can provide clues to its genuineness at first glance.