Black spots on my rock wool???

So i just recently began to germinate my seeds using rock wool, i thought that this method would be best since i will be using a hydro system.

I soaked them in pH adjusted water/nutrient solution yesterday an they have been in a shoebox next to a heater. This morning i took a look at the cubes and saw very small shiny black spots. They almost look like some sort of insect eggs. some cubes have more than others.

So I was going to take out the seedlings and do the papertowel method and put them in a container that wont ket bug in. I have read of other ppl having this happen, is this something that is supposed to happen or do i already have a pest infestation?

It's a burnt by product of the heating and spinning to make the rockwool. Don't quote me but I believe it is volcanic.

Here ya go:

Stonewool products are made from basalt rocks, which come from the Earth. Stonewool is composed roughly of the following elements:
46% Silica, 16% Calcium, 14% Aluminum, 1% Magnesium, 8% Iron, 2% Sodium, 1% Titanium, 1% Potassium, and 1% Manganese (Source: Cultivos vegetales en substratos C.T.I.F.L.) In the production process, a biologically derived binder is used and some lime stone which can leave some lime residue on the surface of the fibers.

Mimicking Mother Nature's production of "angel hair" during volcanic activity, the Grodan Stonewool manufacturer heats rocks to 1600°C, to create lava. The lava is blown into a spinning chamber, which makes fibers similar to cotton candy. These fibers are bagged loosely as "Stonewool granulate". They are also packed into mats, from which Grodan cubes, blocks and slabs are cut. The products make excellent use of natural resources: one cubic yard of rock becomes 37 cubic yards of wool!

so why werent the spots there before? will they only show once soaked? When i soaked them i didn't see any spots, I didn't notice them until this morning. And it seems very inconsistent amongst the cubes. I did use Grodan cubes. I will try and take pics and post them so you guys can see what i am referring to

so being curious i just took some tweezers and examined one of the "dots" and mr mountain high i believe you are correct, the ball appears shiny, and also appears to have almost what looks like threading or fibers coming out of either end as if it had been pulled from something. then when i attempted to crush the tiny black ball i couldn't, it was rock hard. thanks for the insight.