Ow do monopolies effect the price of good

When a company has a monopoly on a product, like diamonds for example, they can set whatever price they want. They limit the amount of products they put out for sale, the higher the demand the less products are put out. So they can jack up the price and we have to pay it in order to get the product. DeBeers has a monopoly on diamonds and they set the price at whatever they want, because they own most of the diamonds in the world. So they can charge what ever they want since there is no competition, or very little competition.