“Beauty often appears in a green dress. We find it often in botany, but green is also very popular in mineralogy and gemology. This is the case with the emerald, for example.”
-quotation from a Portuguese expedition member of Garcia ab Horto, 1565
For a long time, all green stones were grouped together under the name emerald. From a substantial point of view, emerald is a variety of the silicate mineral beryl, which crystallises in the hexagonal crystal system. That is why nowadays only these stones are called emeralds.
The jewel gets its typical green colour from the admixture of chromium and vanadium ions, the line colour is white. If you take a closer look at the density of emerald, it is lighter than ruby, sapphire or diamond.
For example a stone weighing 5 carats will therefore always appear “larger” than a representative of the other three stones listed.
“There is no other gemstone which equals the emerald in beauty and sweetness of colour. Among the green colours, the emerald green is the purest, the happiest fusion of the blue with the yellow, so that neither of these colours stands out. Everyone knows emerald green, the expression has passed into the language of common life: it denotes the true character colour in the series of all green shades.”
This is how Dr. Johann Jacob von Nöggerath, a famous German geologist and mineralogist of the 19th century, describes the gemstone.