Expanded vermiculite looks kind of almost like styrofoam and there are some manufacturers that are using wee bits of styrofoam to replace the more expensive vermiculite.

Polystyrene (styrofoam) beads have been used for a long time in 'some' potting mixes. I've seen it in the plants at the big box stores, etc. Perlite is easy to identify, and vermiculite sort of collapses to mush if you squeeze it when it's wet. It's made from heat-expanded mica...thus, it's puffed up.

Health risks associated with the vermiculite industry has steered potting medium manufacturers to replace it with the beads, is what I hear through the grapevine.

Some years back one mine that produced vermiculite was found to have asbestos in the vermiculite and thre was much concern that people would be exposed to asbestos from that source. That mine was shut down and is no longer in use and no vermiculite comes from there so there is no longer a healthy concern with using vermiculite.

That mine was in Libby, Montana and closed 17 years ago.

Vermiculite is mica rock that has been heated until it expands. The difference in vermiculite vs pearlite is that vermiculite doesn't float which is why I prefer it. There are different grades of vermiculite. Make sure to get yours from a horticultural supplier.

Pearlite is laminated layers of cementite and ferrite formed during the cooling of austenite.

It takes over 500 years for styrofoam to break down so in the big picture, I wouldn't worry about it. You're simply adding aeration to your soil. You're not dumping the contents of a beanbag and you're using common sense. It will do more good in your garden then it will in a landfill.

I've bought some potted plants with the styrofoam bits in the mix. Perlite is also white but is crunchy while styroform of course is spongy in texture.

The other difference between vermiculite and perlite is that once vermiculite is fully saturated it will eventually collapse (in a matter of a few weeks/months) so provides no long-term porosity and aeration. OTOH, perlite will not lose its porosity and is difficult to crush. Fine grades of vermiculite will also create respiratory issues and should be handled with a protective mask.

Neither are recommended as amendments for in-ground plantings but can be beneficial in container soils and as a propagation medium.

Many potting soil mixes on the market today contain as much or more organic material as inorganic material. For example, potting soil can be made of shredded wood, bark, and/or peat moss with minimal amounts of what we call real soil (dirt). Styrofoam pellets, perlite and vermiculite are some of the other items that are often added to the soil mixture for aeration and water retention. In addition, many mixtures also include different types of fertilizers. Some fertilizers are oxidizers, which will make a fire that does start, grow at an even faster rate.

Potting soil mixtures are shipped moist and in plastic bags from the manufacturer. Most people use the soil in their planters in the Spring, then they forget about them once Fall/Winter arrives. Bacterial decomposition occurs within the mix that creates heat. This is the same principle that makes compost piles or bales of hay heat up. Although this principle, which is called spontaneous combustion, is usually found more often in climates containing more moisture; because water acts as a catalyst, these types of fires can also occur here.

But I think Violet is correct "It takes over 500 years for styrofoam to break down so in the big picture, I wouldn't worry about it. You're simply adding aeration to your soil. You're not dumping the contents of a beanbags and you're using common sense. It will do more good in your garden then it will in a landfill."

Luckily for us in the southeast, our local sources of vermiculite have very little asbestos. That is far more a problem with the western deposits.