The name is derived from the colour - the yellow of the lemon - , although the most sought-after stones have a clear, radiant yellowish to brownish red. Like all crystal quartzes, the citrine has a hardness of 7 on the Mohs scale and is thus, to a large extent, insensitive to scratches. It won't immediately take offence at being knocked about either, since its cleavage properties are non-existent. Even if their refractive index is relatively low, the yellow stones have just that mellow, warm tone that seems to have captured the last glow of autumn. Like golden Rhine wine or sparkling Madeira, heavy and sweet, citrine jewelry shimmers and brings a hint of sunshine to those dull November days.