Fülöppite

Fülöppite
Fülöppite-572108 Fülöppite from Baia Mare, Romania
General
Category	sulfosalts
Formula (repeating unit)	Pb3Sb8S15
Strunz classification	2/E.21-50 or 2.HC.10a
Dana classification	03.06.20.01
Crystal system	Monoclinic 2/m, space group C 2/c
Identification
Formula mass	2,076.59 g
Color	Lead-gray; may tarnish steel-blue or bronzy white
Crystal habit	Short prismatic and pyramidal
Fracture	Uneven
Tenacity	Brittle
Mohs scale hardness	2½
Luster	Metallic
Streak	reddish grey
Diaphaneity	Opaque
Specific gravity	5.2
References

Fülöppite is a rare member of the Plagionite Group; other group members are heteromorphite Pb₇Sb₈S₁₉, plagionite Pb₅Sb₈S₁₇ and semseyite Pb₉Sb₈S₂₁. It was named in 1929 for Dr Bela Fülöpp, (1863-1938), a Hungarian lawyer, statesman and mineral collector.

Structure

Fülöppite forms a homologous series with other members of the plagionite group. The structures of these minerals differ by the thickness of a galena sheet which occurs in all of them. Fülöppite has the thinnest such sheet.

Crystallography

Unit Cell Parameters: Z = 4 a = 13.44Å, b = 11.73Å, c = 16.93Å β = 94.7°

Morphology: Crystals short prismatic [201], to 3 mm, and pyramidal; striated on {100} || [0B10] and on{B112} || [110]; curved crystals common (Mindat, HOM). Forms (001), (100), (B101), (112), (111), (B223), (b111), (B221) (AM15)

Appearance

Crystal habits: Short prismatic and pyramidal (All) Colour:Lead-gray; may tarnish steel-blue or bronzy white (AM15, All) Streak: reddish grey ( AM15, Mindat, Webmin, HOM) grey-black (Dana) Lustre: Metallic (All) Diaphaneity: Opaque (Mindat, Webmin, HOM)

Optical Properties

RL Anisotropism (the material appears to change colour when viewed under crossed polarised light in a reflected light microscope) RL Anisotrophism: Moderate in blue-green to red-brown (Mindat, Webmin) May be weak in bluish gray, moderate in blue-green to red-brown (HOM), distinctly anisotropic (Dana)

RL Colour (in reflected plane polarised light) Bronzy white (Webmin), white (Mindat).

Reflectivity in air (540 nm): 31.9 – 40.1% (Dana, Webmin), 36.1–42.0% (HOM)

Physical Properties

Fracture: Uneven (AM15, All except Dana) Tenacity Brittle (All except Dana) Hardness 2½ (All) Specific Gravity measured 5.2, calculated 5.2 (All) Other Characteristics: Fuloppite is not radioactive (Webmin)Melts easily in an open tube yielding sulphur fumes and a deposit of Sb2S2. Not attacked by concentrated hydrochloric acid (AM15)

Occurrence

Type Locality: Dealul Crucii Adit (Crucii Hill; Kreuzberg; Kereszthegy), Baia Mare (Nagybánya), Maramureș Co., Romania (Mindat) Type Material: The Natural History Museum, London, England, 1929,248 (HOM).

Occurrence and Associations Of hydrothermal origin (All except Dana).

Association:Zinkenite, semseyite, Fizélyite, andorite, freieslebenite, geocronite, boulangerite,jamesonite, cinnabar, sphalerite, marcasite, quartz, dolomite (HOM). Fülöppite was first reported in Britain from Wet Swine Gill, Caldbeck Fells, Cumbria. It was described as dark grey metallic patches of fibrous crystals accompanying stibnite. More recently, rare dark red resinous to submetallic subhedral to euhedral crystals associated with stibnite were identified as being close to fülöppite.

Name in Other Languages: German: Fülöppit Russian:Фюлеппит Simplified Chinese: 柱硫锑铅矿 Spanish: Fülöppita