A high quality, permanent, sterile additive with many uses.  See the detailed description.
Vermiculite is the mineral Mica, super-heated to expand much like a accordion. This mineral is often used in soil mixes to increase water holding. Many growers use vermiculite in their flats in order to create a micro environment that will protect seeds from air currents and insulate the seeds to provide uniform germination temperatures.
Ferti-lome Horticultural Vermiculite:

• Is a high quality, permanent additive
• Clean
• Odorless
• Non-toxic
• Sterile
• Light in weight
• Easy to handle
• Easily mixes with potting mix or soil
• Promotes faster root growth
• Provides quick anchorage for young plants