Genealogy / THE MEANING AND RESEARCH OF MY POLISH LAST NAME, SURNAME? [4500]

I am trying to find out anything about my father's Cytryn family. Last year I
discovered my whole family was jewish, and had changed their names after
surviving the Holocaust. My father's real name was Jakub Cytryn, a building
engineer in Warsaw. His father (first name some variant of Mojzesz) was also a
builder. They lived in Warsaw at Leszno 56 in 1939. My father's mother Masza
Guzik was the older sister of David Guzik (JDC Director of Poland during the
war).

I believe the name has to do with quartz stone (english: citrine) rather than
lemons, because I was told a story about my father putting a piece of citrine on
his first wife's grave in Krakow.

Anything you can tell me would be appreciated.

R Baran
NYC