Blaster 61X - What is this junk?

[pmos]

Started tearing down my engine because I sucked in a reed, and saw this in the water jackets surrounding the exhaust port. 61x out a Blaster.

I've got about 7 hrs on the motor, freshwater use only. The material feels chalky, gritty.

It's an SBT rebuild...could this be salt coming out from previous use??

 

[Yami-Rider]

Just calcium build up, seen it on many different motors.