I think there is too much metal in the floor, ie nails for the detector to work. Get a bright LED flash light, dim the lights and slow and methodical search the floor.

Shining a strong flashlight around a darkened room with lights off may help it show up. You could also try placing a nylon stocking or section of old pantyhose over the end of a vacuum cleaner hose wide nozzle attachment and slowly vacuum the entire floor...keep the nozzle close to the floor but not touching it to prevent knocking the earring around...the stocking will trap the earring and keep it from going into the vac bag.

http://cdn.instructables.com/FHW/YBTD/GL...

http://www.instructables.com/id/25-Uniqu...

A metal detector should work... if there's any metal in it at all.

I was bending over to pick something up when I dropped my great grandmother's diamond earring :( I have no idea where it rolled off too, but I know it's in my room. I'm worried it got stuck in one of the cracks between my wooden tiles (I live in a crusty old dorm room). Is there a detector/ a way to recover my earring?