Sorry, can't see the stone. Where did you find it? Did you try taking it to the nearest rock shop or club to see if someone else can help? So far we have a rock weighing just over a pound whick displaces 90 ml. of water which streak tests white and scratches glass. So I can tell you it is hard and heavy for its size.
619 grams divided by 90 cm3 = 6.87 grams per cubic centimeters.