What are the disadvantages of magnetite?

Answer 1

Magnesium metal and its alloys are explosive hazards; they are highly flammable in their pure form when molten or in powder or in ribbon form. Burning or molten magnesium metal reacts violently with water. When working with powdered magnesium, safety glasses with welding eye protection are employed, because the bright white light produced by burning magnesium contains ultraviolet light that can permanently damage the retinas of the eyes.

Magnesium is capable of reducing water to the highly flammable hydrogen gas:

Mg (s) + 2 H2O (l) → Mg(OH)2 (s) + H2 (g)

As a result, water cannot be used to extinguish magnesium fires; the hydrogen gas produced will only intensify the fire. Dry sand is an effective smothering agent but is usable only on relatively level and flat surfaces.

Magnesium also reacts with carbon dioxide to form magnesium oxide and carbon:

2 Mg (s) + CO2 → 2 MgO (s) + C (s)

Hence, carbon dioxide fire extinguishers cannot be used for extinguishing magnesium fires either.
Magnesium hasn't significant disadvantages.

Answer 2

It is quite reactive.

Disadvantages of calcium happen when there is an excess amount that accumulates in the blood. If you are on a thyroid hormone replacement treatment, calcium can interfere with the treatment.