Uplifting, inspirational and generally lovely to have around as it opens up the crown and higher chakras. It is also a great cleanser.
bear in mind that selenite is water soluble so avoid cleansing with water - instead use sound, incense, intention, though in reality it is fairly self-cleansing.
There are 9 hearts approximately the same size with only slight variations. They are 130-201g and are 2-3.5cm x 2.5-3.5cm x 1-2cm, however this does mean some will be slightly smaller/larger. One photo shows the smallest and largest to compare the range