Original description: unknown.
Type locality: Jáchymov (St Joachimsthal), Ostrov, Krušné Hory Mountains, Karlovy Vary Region, Bohemia, Czech Republic and Breitenbrunn, Breitenbrunn District, Erzgebirge, Saxony, Germany.
Type material: unknown.
Etymology: from the Latin to flow, in allusion to its low melting point.
Distribution: notable localities include: Canada: British Columbia, near Grand Forks, Rock Candy mine; Ontario, Madoc; China: Hunan Province, Xianghuapu; England: from many localities in Cornwall; in Durham, as at Weardale; from Castleton, Derbyshire; France: at Bex, Var; on Mont Blanc, near Chamonix, Haute-Savoie; Germany: Wölsendorf, Bavaria, and in the Clara mine, near Oberwolfach, Black Forest; Kazakhstan: Kara Oba; Mexico: from Naica, Chihuahua; and the Ojuela mine, Mapimí, Durango; Namibia: Okorusu; Pakistan: Gilgit district, near Karimabad, at Nagar; Peru: Huanuco, Huanzala; Russia: Dalnegorsk, Nikolaev mine; Spain: Asturias Province, around Berbes; Switzerland: Uri; USA: Colorado, San Juan Co., Sunnyside mine; Illinois, Hardin Co., Rosiclare and Cave-in-Rock; New Mexico, Grant Co., Burro Mountains, Pine Canyon deposit; New York, Monroe Co., Penfield and St. Lawrence Co., Macomb; Ohio, Ottawa Co., Clay Center; Tennessee, Smith Co., Elmwood mine (
Anthony et al., 2001—2005).
Crystal data
Crystallography: isometric — hexoctahedral.
Crystal habit: cubes, octahedra, rarely dodecahedra, or combinations, with many other forms; rounded or stepped, to 2 m; nodular, botryoidal, rarely columnar or fibrous; granular, massive.
Twinning: common on {111}, interpenetrant, flattened (
Anthony et al., 2001—2005).
Physical properties
Cleavage: {111}, perfect (
Anthony et al., 2001—2005).
Fracture: subconchoidal to uneven (
Anthony et al., 2001—2005).
Tenacity: brittle (
Anthony et al., 2001—2005).
Hardness: 4 (
Arem, 1987: 99).
Density: 3—3.25 g/cm
3 (
Lazzarelli, 2012).
Luminescence: fluoresces blue, violet, green, yellow, red under UV; may also be phosphorescent; may be thermoluminescent, or triboluminescent (
Anthony et al., 2001—2005).
Other: slightly soluble in water (0.016 grams per litre at 18°).
Optical properties
Colour: colourless, white, purple, blue, green, yellow, orange; red, pink, brown, bluish black; commonly zoned (
Anthony et al., 2001—2005).
Diaphaneity: transparent to translucent (
Anthony et al., 2001—2005).
Lustre: vitreous, dull (
Anthony et al., 2001—2005).
Refractive index: 1.432—1.436 — isotropic (
Lazzarelli, 2012).
Dispersion: very low — 0.007 (
Arem, 1987: 99).
Pleochroism: none.
