easy to determine that a stone is a humite group mineral, but difficult to determine exactly which member. Other common impurities of clinohumite include aluminium, manganese, and calcium. Formation and occurrence Clinohumite is a product of contact metamorphism and is commonly found as indistinct grains embedded in limestone. Its type occurrence is within the limestone ejecta of the Mount Vesuvius volcano complex near Naples, Italy, where clinohumite was discovered in 1876. The aforementioned gem-quality occurrences of Pamir and Taymyr were discovered only recently: the former in the early 1980s, and the latter in 2000. These deposits are scarce and only sporadically mined, so clinohumite remains one of the rarest gemstones with only a few thousand carats known to exist in private collections. Other (non-gem quality) occurrences of clinohumite include: the Sør Rondane and Balchen Mountains of Antarctica; Mount Bischoff, Waratah, Tasmania; the Saualpe Mountains of Carinthia, the Koralpe mountains of Styria, and the Vals, Virgen, and Ziller valleys of the Tyrol, Austria; the Jacupiranga mine of Cajati, São Paulo State, Southeast Region, Brazil; the Pirin Mountains of Bulgaria; Bancroft, Ontario, Notre Dame du Laus, Wakefield, and Villedieu Township, Quebec, Canada; Southern and Western Finland; Bavaria and Saxony, Germany; eastern Greenland; Ambasamudram in Tamil Nadu, India; Honshū, Japan; Suan, North Korea; Nordland, Norway; KwaZulu-Natal and Northern Cape Province, South Africa; Andalusia, Spain; Värmland and Västmanland, Sweden; Isle of Skye, Scotland; and the states of California, Colorado, Massachusetts, New Jersey, New Mexico, New York, Oklahoma, Utah, and Washington, US. Clinohumite also occurs as a minor component of some masses of peridotite from the Earth's mantle emplaced into the Earth's crust and as a very rare component of peridotite xenoliths. These occurrences and implications have been summarized by Luth (2003) in a discussion of the possible importance of the mineral as a significant reservoir of water in the Earth's mantle. Titanium is a minor constituent of clinohumite in most such occurrences. Clinohumite is stable throughout the upper mantle to depths of at least and is a potential host phase for H (water) in this region of the Earth's interior. Minerals associated with humite include grossular, wollastonite, forsterite, monticellite, cuspidine, fluoborite, ludwigite, dolomite, calcite, talc, biotite, spinel, vesuvianite, sanidine, meionite and nepheline. Crystal structure The structure is monoclinic with space group P21/b (a-unique). The unit cell has a = 4.7488 Å; b = 10.2875 Å; c = 13.6967 Å; and alpha = 100.63°; V