These clusters are called Black Tourmaline Rulers which also called Schorl. These are asrtong black despite the sun making them look bleached in a couple of photos.
It is a good shape for meditating with or laying on your body. Many buy it to protect their front door from energies of negative people living beside them or passing by. Or place below feet in bed to keep out the “naughties” through the night – good feedback from parents with kids frightened in their sleep.
Also consider buying to place on your desk to transmute the office negativity. These black tourmaline rulers have inclusions of mica and/or quartz. They may look a bit white due to the way lighting is reflecting of them. I haven’t found a person yet who doesn’t benefit from tourmaline and this form is particularly popular.
However if you are very sensitive you may find black tourmaline too strong. Buy pink or green tourmaline instead or tourmaline needles inside quartz. If you need a strong piece as it is going to be held or put at the door consider the Madagascan variety.
It is a good idea to buy an amethyst cluster to clean it, if you cannot get it regularly into the sunshine for a clean as it absorbs negativity but doesn’t naturally release it. Dimensions are approximate for the black tourmaline rulers and I will intuit the right one for you,