What is mountain jade?

Mountain jade refers specifically to jadeite that is found in a certain geological setting, typically associated with thick-skinned jadeite boulders. This type of jadeite is known for forming under high-pressure and high-temperature conditions within the earth's crust, often resulting in boulders that can be quite large and hefty. These jadeite boulders are prized for their quality and can exhibit beautiful colors and textures.

The other options do not accurately describe mountain jade. Lightweight synthetic jade refers to a man-made material, which is fundamentally different from natural mountain jade. Thin, polished jadeite sheets suggest processed jade rather than the raw, natural form of mountain jade. A type of emerald found in mountainous regions significantly diverges from the definition of jade, as emeralds are a different mineral altogether. Thus, the identification of mountain jade as thick-skinned jadeite boulders is precise in its geological and material context.