Search Mineralpedia – A Mineral Photo Database and Identification Guide
Named after John Bernard Jago Trelawney, who was an American mineral collector from California, USA and was a great benefactor of mineral collections. Jagoite is a rare mineral that occurs in hematite ore in metamorphosed iron-manganese orebodies in only one locality in the world at Langban in Sweden. Associated minerals include melanotekite and quartz.
Ref. Handbook of Mineralogy, Anthony et al (1995) and MSA at http://www.handbookofmineralogy.org/pdfs/jagoite.pdf
Named for John Arthur Gower, a fomer Professor of Mineralogy at the University of British Columbia in Vancouver, Canada. Jagowerite is a rare mineral that can be found in only in the Hess River area in the Mayo Mining District of Yukon Territory, Canada. There, it is found in quartz veins that are filling tension fractures in carbon-rich argillite. Associated minerals include pyrite and hinsdalite. Jagowerite will fluoresce a greenish-white under long-wave ultraviolet light.
Ref. Handbook of Mineralogy, Anthony et al (1995) and MSA at http://www.handbookofmineralogy.org/pdfs/jagowerite.pdf
Named for Richard H. Jahns (1915-1983). Occur predominately in zoned pegmatites. At the type locality, the Tip Top mine near Custer South Dakota, crystals occur as light to dark brown, deep red-brown and red-orange, vitreous, short to long prismatic crystals to 7mm. Crystals are striated length-wise on the prism face  and are typically tabular and found as singles and subparallel groups in altered Triphylite matrix with Leucophosphite, Rockbridgeite, Hureaulite and Tavorite. Jahnsite (CaMnMg) has not been found in association with Jahnsite (NaFeMg), which occurs in Heterosite matrix.
For best reference see unpublished Thomas Campbell MS thesis, SDSM&T 1984.
Ref. Handbook of Mineralogy, Anthony et al (1995) and MSA at http://www.handbookofmineralogy.org/pdfs/jahnsite-(CaMnMg).pdf
Jahnsite - (NaFeMg) occurs in at the Tip Top pegmatite west of Custer, South Dakota. Thus far it has been a one-time find. Crystals occur as 1mm pseudo-orthorhombic twinned prisms to 1mm in tiny vugs within Heterosite with dark purple Leucophosphite and Dufrenite. The crystals are translucent yellow with orange bands near the termination. Two other new Jahnsites (NaMnMg) and (CaMgMg) are present in the crystals but can be characterized due to insufficient volumes.
Ref. Kampf, A.R., Steele, I. M., Loomis, T. A. Am.Min. 93,940-945(2008).