there is a big difference between silica and magnesium in structure-function and reactivity. Mg is ruled by the sun and is essential salt in the human body in DNA, RNA metabolism and repair and in the nervous system.
Silica is prominent in the mineral kingdom and oceans. There is an old article from Isaac Asimov comparing why life is made from carbon vs. silica - both are tetravalent. The conclusion was that the that C-H vs Si-H was more labile and appropriate for evolution on this planet.
Hower, according to Dubuis the next higher intelligence above us is based on Si - think on what all the computers run. The scariest thing for me is the self-replicating nanorobots. Just think about modern life and how much Si is surrounding you - computer, TV, alarm clock, car, plane - camera not to menton d boobs, rsrs.
I am interested in it cuz it is a matrix, womb that catalizes metallic transformations and has very interesting properties, the most important being able to transmit and store LIGHT and electricity- in other words - INFORMATION - fiberoptics. Mg is much more reactive cmpared to it. Simply melts, oxidizes and probably transmutates. But without it our DNA wouldnt associate and out nerves wouldnt work. Two very different things