Identificación de minerales y menas en campo usando dureza, raya, brillo, clivaje, hábito cristalino y pruebas químicas simples. Cubre la metodología de eliminación sistemática, aplicación de la escala de Mohs e indicadores comunes de menas para metales preciosos, piedras preciosas y minerales industriales. Usar al encontrar un espécimen de roca o mineral desconocido, al prospectar y evaluar si un sitio muestra indicadores de minerales valiosos, al distinguir roca portadora de mena de roca estéril en campo, o al desarrollar alfabetización geológica mediante observación sistemática.
Identificar minerales en campo usando propiedades físicas, eliminación sistemática y pruebas de campo simples.
Antes de manipular, observar el espécimen en contexto.
Field Context:
+--------------------+------------------------------------------+
| Observation | Record |
+--------------------+------------------------------------------+
| Host rock | What type of rock is it in/on? |
| | (granite, basite, sandstone, schist...) |
+--------------------+------------------------------------------+
| Geological setting | Vein, disseminated, massive, placer, |
| | weathering surface, cave deposit |
+--------------------+------------------------------------------+
| Associated | What other minerals are nearby? |
| minerals | (quartz veins often host gold; iron |
| | staining suggests oxidation zone) |
+--------------------+------------------------------------------+
| Crystal form | Visible crystals? Habit? Size? |
| (if visible) | (cubic, prismatic, tabular, massive) |
+--------------------+------------------------------------------+
Esperado: Contexto de campo registrado antes de manipular el espécimen.
En caso de fallo: Si el contexto geológico no es claro (espécimen suelto, hallazgo urbano), proceder solo con las propiedades físicas — el contexto habría ayudado a reducir candidatos pero no es estrictamente requerido.
Aplicar las pruebas diagnósticas sistemáticamente.
Diagnostic Property Tests:
LUSTER (how it reflects light):
- Metallic: reflects like metal (pyrite, galena, gold)
- Vitreous: glassy (quartz, feldspar)
- Pearly: like a pearl (muscovite, talc surfaces)
- Silky: like silk fibers (asbestos, satin spar gypsum)
- Earthy/dull: no reflection (kaolin, limonite)
- Adamantine: brilliant, diamond-like (diamond, zircon)
HARDNESS (Mohs scale — scratch test):
+------+-----------+----------------------------------+
| Mohs | Reference | Can Be Scratched By |
+------+-----------+----------------------------------+
| 1 | Talc | Fingernail |
| 2 | Gypsum | Fingernail (barely) |
| 3 | Calcite | Copper coin |
| 4 | Fluorite | Steel nail (easily) |
| 5 | Apatite | Steel nail (just) |
| 6 | Feldspar | Steel nail cannot scratch |
| 7 | Quartz | Scratches glass |
| 8 | Topaz | Scratches quartz |
| 9 | Corundum | Scratches topaz |
| 10 | Diamond | Scratches everything |
+------+-----------+----------------------------------+
Test: try to scratch the specimen with each reference tool,
starting from soft to hard. The hardness is between the tool
that fails and the tool that succeeds.
STREAK (powder colour on porcelain):
- Drag the specimen firmly across an unglazed porcelain tile
- Record the colour of the powder line
- Streak colour is often different from specimen colour
- Critical: hematite is grey-black but streaks RED
- Critical: pyrite is gold but streaks BLACK
- Minerals harder than the streak plate (~7) will not leave a streak
CLEAVAGE AND FRACTURE:
- Cleavage: breaks along flat planes (mica: 1 direction, feldspar: 2)
- Fracture: breaks irregularly (conchoidal = curved like glass, uneven, fibrous)
- Note number of cleavage directions and angles between them
SPECIFIC GRAVITY (heft test):
- Hold the specimen and assess: does it feel heavier or lighter
than expected for its size?
- Heavy: possible metallic ore (galena, gold, magnetite)
- Light: possible pumice, sulfur, or organic material
Esperado: Un perfil del espécimen: brillo, rango de dureza, color de raya, tipo de clivaje/fractura y densidad relativa.
En caso de fallo: Si una propiedad es ambigua (ej., brillo entre metálico y vítreo — "sub-metálico"), registrar ambas opciones. La ambigüedad reduce la confianza pero no impide la identificación.
Pruebas adicionales para grupos minerales específicos.
Special Field Tests:
MAGNETISM:
- Hold a magnet near the specimen
- Strong attraction: magnetite (or possibly pyrrhotite)
- Weak attraction: some iron-bearing minerals
ACID TEST (10% HCl):
- Drop acid on the specimen surface
- Vigorous fizzing: calcite (CaCO3)
- Fizzing on powder only: dolomite (scratch surface first, then apply acid)
- No fizzing: not a carbonate
TASTE (only for suspected halite):
- Salty taste: halite (NaCl)
- Do NOT taste unknown minerals generally — some are toxic
SMELL:
- Sulfur: rotten egg smell (sulfides when scratched)
- Clay: earthy "petrichor" smell when breathed on (clay minerals)
TENACITY:
- Brittle: shatters when struck (most silicates)
- Malleable: deforms without breaking (gold, copper, silver)
- Flexible: bends and stays (chlorite, some micas)
- Elastic: bends and springs back (muscovite mica)
Esperado: Datos diagnósticos adicionales que reducen aún más la identificación.
En caso de fallo: Si las pruebas especiales no están disponibles (sin imán, sin ácido), proceder con las propiedades básicas — son suficientes para la mayoría de los minerales comunes.
Verificar cruzadamente el perfil de propiedades contra minerales conocidos.
Common Mineral Identification Key (simplified):
METALLIC LUSTER:
- Black streak + hard (6+) + cubic crystals = PYRITE
- Black streak + soft (2.5) + heavy + cubic = GALENA
- Red-brown streak + hard (5-6) + heavy = HEMATITE
- Yellow streak + soft (1.5-2.5) + yellow = GOLD (if malleable)
or CHALCOPYRITE (if brittle, harder, green-black streak)
- Black streak + magnetic = MAGNETITE
NON-METALLIC, LIGHT-COLORED:
- Vitreous + hard (7) + conchoidal fracture = QUARTZ
- Vitreous + hard (6) + 2 cleavage planes = FELDSPAR
- Vitreous + soft (3) + fizzes in acid = CALCITE
- Pearly + very soft (1) + greasy feel = TALC
- Vitreous + soft (2) + 1 perfect cleavage = GYPSUM
NON-METALLIC, DARK-COLORED:
- Vitreous + hard (5-6) + 2 cleavage at ~90 degrees = PYROXENE
- Vitreous + hard (5-6) + 2 cleavage at ~60/120 degrees = AMPHIBOLE
- Vitreous + soft (2.5-3) + 1 perfect cleavage + flexible = BIOTITE (mica)
Esperado: Una identificación mineral o una lista corta de 2-3 candidatos con la prueba diferenciadora necesaria para distinguirlos.
En caso de fallo: Si el espécimen no coincide con ningún mineral común, puede ser una roca (agregado de minerales) en lugar de un mineral único, o puede requerir análisis de laboratorio (sección delgada, DRX).
gold-washing — la recuperación de oro aluvial usa habilidades de identificación mineral para leer depósitos de arroyos y evaluar gravas auríferas