A period is a bleed from the womb (uterus) that is released through the vagina. It happens approximately every 28 days, although anywhere between 24 and 35 days is common. Periods can begin when girls are between 8 and 16 years old, but usually start around the age of 12.
Emerald is a gemstone and a variety of the mineral beryl (Be3Al2(SiO3)6) colored green by trace amounts of chromium and sometimes vanadium. Beryl has a hardness of 7.5â8 on the Mohs scale. Most emeralds are highly included, so their toughness (resistance to breakage) is classified as generally poor.
Emerald has priority over beryl as a mineral name. Emerald was known in antiquity and was prized as a gem. In the 1790s, Louis Nicolas Vauquelin, the discoverer of chromium, demonstrated that emerald and beryl were essentially the same chemical compound and that emeralds, sensu strictu, contained chromium.