SiO2-Si-MgSi-SiO2

The order of the compounds you mentioned represents a sequence of silicates, which are minerals composed of silicon, oxygen, and other elements.

SiO2, also known as silicon dioxide or quartz, is the most basic and common form of silica. It is a major component of many rocks and minerals.

Si-MgSi, also known as magnesium silicate or talc, is a silicate mineral that contains both silicon and magnesium. It has a soft and smooth texture and is commonly used in cosmetics and as a lubricant.

MgSi-SiO2, refers to a combination of magnesium silicate and silicon dioxide. The exact composition and characteristics of this compound would depend on the specific ratio and structure of the silicon dioxide and magnesium silicate components.

Overall, this sequence represents different forms and combinations of silicate minerals, each with its distinct properties and uses.