Brown crusty stuff on heater

[ckrause]

I have built up brown crusty stuff on my heater glass. Does anyone know what it is?
It is only on the glass and nowhere else in my tank.

http://www.flickr.com/photos/a98gsxr/6103595456/in/photostream

http://www.flickr.com/photos/a98gsxr/6103049519/in/photostream

http://www.flickr.com/photos/a98gsxr/6103050545/in/photostream

I rubbed it with my fingers and it didn't fade or come off. It looks like it's burned on rock.

Any help is greatly appreciated

Chuck

 

[axelrod12]

Was your heater left on out of the water

 

[ckrause]

No it wasn't. I scraped it off with a razor blade so now it is gone for now. Still don't know what it could have been though.

 

[SubRosa]

Mineral deposits