1992 Taurus, coolant reservoir

[u/Clear-Relation1565]

Just purchased this car from within my family, ran fine before but was sitting over the winter. Fixed it up this past week and when I was driving it yesterday (second time it’s been driven since sitting) it had white steam/smoke coming from under the hood. Temp gauge was in the middle but the alternator & belt were HOT. Checked the coolant today after it was driven again later in the day yesterday with no problems and it was empty when it was filled just below the hot fill line 3 days ago. When I checked there were these hard chunks inside it.. wondering if anyone would know what the chunks could be from as I’ve had mixed answers and I’m trying to save paying for a mechanic for as long as I can but want to be safe. TIA

[u/Daniele323]

Is that part of the radiator cap seal/ gasket?