Silica = silicon = silicon dioxide. It's extremely common in the earth's crust in silica-rich rocks such as obsidian, granite, and sandstone. Feldspar and quartz are the most significant silicate minerals. Silicon also alloys with a variety of metals, including iron, aluminum, copper, nickel, manganese. It's often used in foods as an anti-caking agent, so it isn't likely to harm you unless you breathe the dust, which can put you at risk for respiratory issues like silicosis.

Wear a mask, as you should when you are working with sphagnum moss, perlite, pine bark, and other soil products that contain dust you could inhale. Moistening it as soon as it's feasible in soils also considerably reduces any risk.

Al

deric i did same thing this weekend.i beleive the difference may b just particle size.after finding this less expensive version i am going to run with mels mix.by the way i found the peat for the recipe least expensive at walmart for the 3.8 cu. ft. bag around 10$ a bag.be sure to have good venilation when mixing these 2.im sure well get responses about the recipe good luck,have fun!!

I should have mentioned that vermiculite and perlite NOT intended for horticultural applications is often treated with hydrophobic (water repellent) chemicals (even insecticides and DE) - especially the material intended for use as building or masonry insulation. It may not be the best idea to use other than hort grade materials.

Al

The horticultural vermiculite also comes in medium and coarse, I'd recommend the coarse as it will hold up a bit longer.