Vermiculite is a naturally occurring mineral that takes the form of glossy flakes, varying in color from dark gray to sandy brown. These flakes, which are more specifically a hydrated magnesium iron aluminum silicate mineral, get heated up in a purpose-built commercial furnace, where they then expand and take on a concertina shape, almost like a tiny accordion.
It is this version of vermiculite that is used in horticulture most commonly as a means of improving soil quality or giving seedlings a helping hand to root more quickly.
 
If you’re looking for an additive to improve the quality of your soil, or even entirely replace the soil, then vermiculite is an attractive option. It is commonly used in soil mixes, as well as by professional gardeners and nursery workers to improve seed germination success and encourage rapid root growth in cuttings.
It can also be invaluable in preventing plants from being overwatered and succumbing to root rot, as it has impressive moisture retention properties that release water in line with the plant’s needs.