100 year old lamp

I don't know exactly how old this lamp is but my family got it from a neighbor who was in her 80's about 30 years ago. We have reasonably estimated that the lamp is 100 years old. It used to be in a dentist's office and was moved into our house. It is in good but dirty condition. I was wondering about the worth because my neighbor offered me $300 for it. Also the base seems to be some sort of marble or heavy smooth rock.