Nature's Steampunk Gears: How Bournonite Twinned at 88.6° Into Mirror 'Cogwheels' in Cornwall & Hunan
PbCuSbS3 Orthorhombic Cyclic Wheels • {110} Contact Gear Teeth • Herodsfoot UK vs Yaogangxian (60FPS)
Pull a bright gunmetal specimen out of Cornwall's historic Herodsfoot Mine or China's tungsten vaults at Yaogangxian and swear someone bolted precision machined brass-steel spur gears straight onto Quartz rock! Chemically a dense Lead-Copper-Antimony sulfosalt (PbCuSbS3, SG 5.83), Orthorhombic Bournonite possesses an unusual unit-cell diagonal almost dead on 45° (~88.6° twin angle!), forcing repeated {110} twin sectors to interlock crosswise with radiating corner notches that look uncannily like crisp mechanical Cogwheel Gears! Snap gear teeth live across 1–4 cyclic crossings, test Lead-Copper-Antimony luster, and separate real Cogwheels from blocky Tetrahedrite and Galena!
Wait — Did You Know?Flooded way back in 1884, Cornwall's legendary Herodsfoot Mine near Liskeard stunned Victorian Britain with crisp multi-toothed metallic cogwheels sitting flat on snowy white Quartz and honey Siderite—turning Bournonite ('Wheel Ore') into an instant collector obsession!
Select Specimen or Control Sample (8 Profiles)
Click any classic Bournonite gear wheel, Peruvian thick block, or metallic lookalike to check twin teeth & cleavage:
Cycle twinning from Single Block -> Cross Twin -> Full Stacked Cogwheel to watch natural Orthorhombic teeth snap cleanly around 88.6°!
{110} Cyclic Twin Branches (1–4)4 cycles
Cogwheel Spur Tooth Depth85%
Gunmetal Specular Shine88%
PbCuSbS3 Gear Twinning, Density & Luster Telemetry
Live Diagnostic Telemetry
{110} Gear Teeth & HabitMohs 2.8 | SG 5.83
Hardness / Specific GravityMirror Gunmetal Spur Wheels!
Classic Locality & ContrastPerched On Cream Siderite & Quartz!
Watch The Center Seam: Real natural cogwheels NEVER look cleanly cut from single lathe steel—fine twin junction lines cut cleanly into gear hubs!
Why does this happen atom-by-atom? Read the 3-step physics strip below, then keep scrolling for Chapter 2 (Microscopic Atomic Zoom) and Chapter 3 (Interactive Real vs. Fake Split Loupe).
With unit-cell ratio a/b ~ 0.94 creating diagonal ~88.6° angles, flat blocky PbCuSbS3 crystals align right near cubic symmetry without becoming true cubes.
2. Repeated {110} Contact Twinning Pivots Crystals ~90° Around A Hub
When each newly nucleated crystal blade locks along the {110} face rotated ~88.6°, protruding rectangular corners repeat cyclically outward—sculpting real metallic gear teeth!
Real museum cogwheels stay totally non-magnetic, weigh dense at SG 5.83, and display fine twin junction grooves intersecting right through center faces.
Chapter 2 of 3 • Microscopic Atomic Lattice Zoom
Inside The Lattice: Liskeard Herodsfoot Cornwall Wheel Bournonite
❌ MYTH: Bournonite's weirdly notched round 'Cogwheels' were machined or acid-carved by collectors.
✅ FACT: 100% genuine crystallography! Cyclic twinning along {110} (~88.6°) physically rotates consecutive Orthorhombic plates around a single axis so rectangular block corners poke symmetrically outward like precision gear teeth!
❌ MYTH: Shiny steel-grey Bournonite must be almost as hard and durable as stainless steel.
✅ FACT: Don't scratch it with pins! Packing soft Lead (42%) and Antimony, pure Bournonite is gentle Mohs 2.5–3.0—far softer than steel knives and brass pins!
❌ MYTH: Any gray metallic cube-like crystal sitting on Yaogangxian Quartz & Fluorite is Galena.
✅ FACT: Check edges closely under 10x: Yaogangxian hosts very little Galena beside Fluorite—those stunning heavy mirror-bright serrated wheels are classic PbCuSbS3 Bournonite!
Chapter 3 of 3 • Interactive Real vs. Fake Split Loupe
Authentic Specimen vs. Fake / Impostor Drag-Loupe
Drag the divider left/right — toggle Probe Mode for forensic lighting, cleavage & bubble inspection.
60-Second Pocket Field Test Checklist
Examine circumference teeth under 10x: look for natural variation in tooth depth PLUS crisp straight diagonal twin boundary seams slicing cleanly inward across flat metallic faces!
Test gently near an N52 magnet: real Bournonite has ZERO iron magnetism (ruling out painted iron watch cogs or Magnetite immediately).
Notice palm density & non-90° break: heavy SG 5.83 (lighter than Galena 7.58, heavier than Sphalerite 4.0) with shiny conchoidal fractures instead of 90° Galena cubes.
Always wash hands thoroughly after touching bare Lead-Antimony sulfosalts and keep specimens boxed safely away from ultrasonic baths and damp acid cleaners.
Collector Caution & Fake Alert: HEAVY METAL & ULTRASONIC WARNING: Packing ~42% Lead and ~25% Antimony by weight alongside soft Mohs 2.8 fragility, raw Bournonite dislikes acidic dips, abrasive polishing, AND ultrasonic tanks! Wash hands promptly with soap after touching unsealed PbCuSbS3 pieces and keep specimens safely bone-dry.
Collector Field Guide & Mineralogy Deep Dive
Locality, Chemistry & Optical Notes
🇬🇧 1850s Cornwall: Flooding Of The Iconic Herodsfoot Mine
Carved down through Devonian slate near Liskeard, Cornwall's Herodsfoot lead-silver mine closed permanently in 1884—leaving behind priceless Victorian cabinet drawers packed with razor-sharp gunmetal Cogwheels sitting proudly atop pearly Siderite & Chalcopyrite!
🇨🇳 Yaogangxian 2000s: China Re-Writes The Cogwheel Scalebar
Long limited to ~1–2 cm European rarities, China's Yaogangxian mine shocked Tucson mineral halls with gleaming mirror-chrome Bournonite cogwheel towers topping 5–7 cm perched beside gemmy ice-blue Fluorite cubes!
Whenever you superimpose two nearly square rectangles rotated slightly off 90° (or shifted across {110} twin boundaries), four corners stick out cleanly while tiny V-valleys notch symmetrically between them—repeating 3–4 cycles turns geometry straight into a mechanical gear!
🧼 Keeping Lead Sulfosalts Gleaming Without Harsh Solvents
Avoid strong HCl/vinegar carbonate dissolves when carbonate dust coats Bournonite: harsh acid clouds mirror steel surfaces forever! Clean gently using dry artist sable brushes and keep RH reasonable.
Diagnostic Specimen Comparison Matrix
Quick Laboratory & Collector Reference
Mineral / Control
Formula & System
Key Physical Metric
Diagnostic Tell
Classic Locality
Herodsfoot Cogwheel
PbCuSbS3 {110} Cyclic
Mohs 2.8 | SG 5.83
Historic multi-toothed British gunmetal wheel
Liskeard, Cornwall UK
Yaogangxian Bournonite
PbCuSbS3 Mirror Wheel
Mohs 2.8 | Up to 6 cm
Razor mirror chrome gears w/ Fluorite & Qtz
Hunan, China
Harz 'Rädelerz' Twin
PbCuSbS3 Cross Twin
Mohs 2.8 | SG 5.83
Original 2-cycle cruciform wheel root
Neudorf, Germany
Swiss Seligmannite
PbCuAsS3 | Isomorph
Mohs 3.0 | SG 5.44
Miniature Arsenic gear twins in white dolomite
Binntal, Switzerland
Pure Galena Control
PbS | Cubic Fm-3m
Mohs 2.5 | SG 7.58
No gear teeth; heavier weight; 90° step cleavage
Non-Sb/Cu Lookalike
Scrap Watch Gear Fake
Iron-Carbon Steel Alloy
Magnetic! Lathe-Cut
Snaps onto magnets + identical machined teeth
Novelty Assembly
Frequently Asked Mineralogy Questions
Collector & Lab Answers
How do natural Bournonite crystals form shapes that look like machined metal gear cogwheels?
Bournonite crystallizes in an Orthorhombic cell whose diagonal angle measures ~88.6°. Repeated {110} contact twinning pivots consecutive crystal blocks around a central axis so rectangular corners protrude evenly outward into serrated gear teeth!
Where do the world's finest Cogwheel Bournonite specimens come from?
Historically Cornwall's Herodsfoot Mine (UK, closed 1884), Neudorf (Germany), and Machacamarca (Bolivia) produced museum classics; since the 2000s, China's Yaogangxian Mine has yielded the world's largest mirror-bright giant Cogwheels.
How can I tell real Bournonite Cogwheels apart from Galena or Tetrahedrite?
Unlike simple mirror cubes (Galena, 90° step cleavage, SG 7.58) or 3-sided pyramids (Tetrahedrite, zero gear teeth), Bournonite displays notched rectangular/cyclic spur gear rims, diagonal twin junction seams, zero 90° cube cleavage, and SG 5.83.
What is Seligmannite and how does it relate to Bournonite?
Seligmannite (PbCuAsS3) is the rare Arsenic twin analog of Antimony-bearing Bournonite (PbCuSbS3)—crystallizing in identical tiny cogwheel shapes inside Switzerland's snow-white Lengenbach dolomite.
Is Bournonite strong and safe to wash in ultrasonic cleaners?
No! Packing ~42% Lead and Antimony at soft Mohs 2.5–3.0, Bournonite shatters delicate corners in ultrasonic tanks and tarnishes in strong acids. Always dust dry and wash hands thoroughly afterward.