Serpentine subgroup (part of the kaolinite-serpentine group in the category of phyllosilicates)[1] are greenish, brownish, or spotted minerals commonly found in serpentinite.

Serpentine minerals are polymorphous, meaning that they have the same chemical formulae, but the atoms are arranged into different structures, or crystal lattices.

[8][9] Most serpentines are opaque to translucent, light (specific gravity between 2.2 and 2.9), soft (hardness 2.5–4), infusible and susceptible to acids.

[10] The second level of the structure organized into different serpentine species originates partly to compensate the intra-layer stress due to this dimensional misfit.

Good compensation results in a nearly constant layer curvature, with the larger octahedral sheet on the convex side.

Antigorite is the polymorph of serpentine that most commonly forms during metamorphism of wet ultramafic rocks and is stable at the highest temperatures—to over 600 °C (1,100 °F) at depths of 60 km (37 mi) or so.

Occurrence is worldwide, notable localities include New Caledonia, Canada (Quebec), US (northern California, Rhode Island, Connecticut, Massachusetts, Maryland and southern Pennsylvania),[16] Afghanistan, Britain (the Lizard peninsula in Cornwall), Ireland, Greece (Thessaly), China, Russia (Ural Mountains), France, Korea, Austria (Styria and Carinthia), India (Assam, and Manipur), Myanmar (Burma), New Zealand, Norway and Italy.

The asbestos content can be released into the air when serpentine is excavated and if it is used as a road surface, forming a long-term health hazard by breathing.

Asbestos from serpentine can also appear at low levels in water supplies through normal weathering processes, but there is as yet no fully proven health hazard associated with use or ingestion, although the EPA states an increased risk of developing benign intestinal polyps can occur.

The more attractive and durable varieties (all of the antigorite) are termed "noble" or "precious" serpentine and are used extensively as gems and in ornamental carvings.

The town of Bhera in the historic Punjab province of the Indian subcontinent was known for centuries for finishing a relatively pure form of green serpentine obtained from quarries in Afghanistan into lapidary work, cups, ornamental sword hilts, and dagger handles.

[9] This high-grade serpentine ore was known as sang-i-yashm in Persian, or 'false jade' in English, and was used for generations by Indian craftsmen for lapidary work.

The Māori of New Zealand once carved beautiful objects from local serpentine, which they called tangiwai, meaning "tears".

Bowenite, a variety of antigorite, is an especially hard serpentine (5.5) of light to dark apple green color, often mottled with cloudy white patches and darker veining.

Williamsite is an American local varietal name for antigorite that is oil-green with black crystals of chromite or magnetite often included.