Finding charcoal, glass, with md, why?

[trooper531]

I have watched YouTube extensively and was wondering why people are finding charcoal and glass with a metal detector? Yes I am VERY new to this, have had my Garrett Ace 400 2 weeks now and waiting for the ground to thaw here in lower Michigan. Thank you!!

 

[digger27]

Metal detectors won't pick up glass.

What looks like charcoal could be what we call coal clinkers or something called hot rocks.
There are enough minerals in these types of problem targets that they can disturb the ground balance of our detectors so they pick them up as metal.

Read this.
Hot Rocks

 

[villagenut]

A lot of trash pits and old dumping sites will be littered with broken glass as well as burnt coal from the stove...all thrown in a hole together along with small iron and other refuse.