TRABAJO PRÁCTICO N°4TRABAJO PRÁCTICO N°4

CABONATOS, SULFATOS, FOSFATOS, WOLFRAMATOS

GRUPOS MINERALES

1. Elementos nativos2. Sulfuros3. Sulfosales4. Óxidos   (a) Simples y múltiples   (b) Hidróxidos5. Haluros6. Carbonatos7. Nitratos8. Boratos9. Fosfatos10. Sulfatos11. Wolframatos12. Silicatos

CARBONATOS

• Dureza 3 a 5

• Habitualmente colores claros

• Brillo no metálico

• se dividen en grupos:– Grupo de la Calcita (Trigonal) sin grupos OH– Grupo de la Aragonita (Rómbica) sin grupos OH– Grupo de la Dolomita (Trigonal) sin grupos OH– Carbonatos con grupos OH (Monoclínicos)

CARBONATOS

• los carbonatos sin grupos (OH) forman mezclas isomorfas y sales dobles.

CALCITA CaCO3 (TRIGONAL)

Clivaje rombohédrico perfecto (75°)

Brillo vítreo

Dureza 3

Cristales prismáticos, tabulares, agregados granulares, agregados fibrosos, etc.

Raya blanca

Con ClH desprende CO2

SIDERITA FeCO3 (trigonal)

• Clivaje rombohédrico perfecto

• Dureza 3,5-4

• Color castaño oscuro a claro

• Alto P.E.

RODOCROCITA MnCO3 (Trigonal)

• Color rosa a rojo

• Bandeada

• Dureza 4

• Raya blanca

• Brillo vítreo

• En masas granulares, laminares o botroidales y en costras

DOLOMITA CaMg(CO3)2 (Trigonal)

• Clivaje rombohédrico perfecto

• Color pardo, blanquecino

• Puede reaccionar levemente con ClH

• Raya blanca

• Brillo vítreo

ARAGONITA CaCO3 (Rómbico)

• Clivaje imperfecto

• Color verde, amarillento, pardo

• Cristales aciculares

• Agregados fibrosos, coraloides, estalactíticos

• Nácar de moluscos, perlas. Precipita a partir de aguas calientes carbónicas en grutas, manantiales hidrotermales. A P y T ambiente se transforma lentamente en su polimorfo Calcita

Malaquita Cu2(Co3) (OH)2 (Monoclínico)

• Agregados masivos, bandeados, fibrosos, pátinas, etc.

• Color verde

• Zona de alteración de yacimientos cupríferos

Malaquita Cu2(Co3)

(OH)2

Azurita Cu3(CO3)2(OH)2

(Monoclínico)

• Agregados terrosos, en pátinas, masivos.

• Color azul

• Alteración de sulfuros de cobre.

Azurita Cu3(Co3)2(OH)2

SULFATOS

• Habitualmente colores claros

• Brillo no metálico

• se dividen en grupos:– Anhidros o Grupo de la Baritina (Rómbico)– Hidratados: Yeso (Monoclínico)

BARITINA BaSO4 (Rómbica)

• Cristales tabulares

• Alto P.E.

• Brillo vítreo

• Color blanco o pardo claro

CELESTINA SrSO4 (Rómbica)

• Color celeste, blanco, gris

• Cristales tabulares

• Más liviana que la baritina

• Raya blanca

• Brillo vítreo

YESO CaSO4· 2H2O (monoclínico)

• Dureza 2

• Brillo vítreo, perlado, sedoso

• Incoloro, blanco, gris

• En cristales tabulares de gran tamaño. En masas micáceas transparentes (Espejuelo), masivo o finamente granular (Alabastro). Son frecuentes las formas fibrosas en largos cristales alargados. Frecuentes maclas en punta de flecha o lanza.

The largest natural crystals on Earth have been discovered in two caves within a silver and zinc mine near Naica, in Chihuahua, Mexico, according to mine officials. Reaching lengths of 15m, the clear, faceted crystals are composed of selenite, a crystalline form of the mineral gypsum.

The Naica Mine of Chihuahua, Mexico, is a working mine that is known for its extraordinary crystals. Naica is a lead, zinc and silver mine in which large voids have been found, containing crystals of selenite (gypsum) as large as 1.2 m in diameter and 15 m long. The chamber holding these crystals is known as the Crystal Cave of Giants, and is approximately 300 m down in the limestone host rock of the mine. The crystals were formed by hydrothermal fluids emanating from the magma chambers below. The cavern was discovered while the miners were drilling through the Naica fault, which they were worried would flood the mine. The Cave of Swords is another chamber in the Naica Mine, containing similar large crystals.

Largest Selenite Crystals In The

World

He said that the sight was beautiful “…like light reflecting off a broken mirror”. The translucent crystals lie pitched atop one another, as though moonbeams suddenly took on weight and substance. One month later, another team of Naica miners found an even larger cavern adjacent to the first one.

"Walking into either of these caves is like stepping into a gigantic geode," said Richard D. Fisher, an American consultant with the mining company to develop the discoveries as tourist attractions. Fisher said that most people can endure only a few minutes in the caves due to their high temperatures.

The smaller of the two caves, which is about the size of two-bedroom apartment, is 38°C. The large chamber, which Fisher describes as the size of a Cathedral, is 65°C. Both are located approximately 360m below the surface.

The largest previously known crystals were found in the nearby Cave of the Swords, part of the same mine system. Some of these are now on display at the Smithsonian Institution. The local government and mine owners hope to avoid removing any of the new discoveries for museum displays or private collections, Fisher said.

While the mine company is currently limiting visitation of the caves to scientific experts, mineral hunters have destroyed locks and broken into the chambers twice since they were first opened by mining equipment last April. One man was killed when he attempted to chop out a gigantic crystal that fell from the ceiling and pinned him.”The heat did him in” according to Fisher.

"We need more onsite protection of mine caves," said geologist Carol A. Hill, co-author of the book Cave Minerals of the World, who calls the new discoveries "by far the largest selenite crystals I have ever heard of."

Hill applauds the tourism plan. "Without it, the mining company would probably destroy the caves. Museums have enough crystals," she said. "It's important to preserve discoveries like this where they occur."

The mining company plans to air-condition the caves before opening them to the public next year, Fisher said. He adds that reducing the heat gradually will not harm the crystals.

Officials of the Penoles Company, which owns the mine, kept the discoveries secret out of concern about vandalism. Not many people, however, would venture inside casually: the temperature hovers at 65 degrees, with 100 percent humidity. A person can stay inside the cave for only six to ten minutes before becoming disoriented.

Groundwater in these caves, rich with sulfur from the adjacent metal deposits, began dissolving the limestone walls, releasing large quantities of calcium. This calcium, in turn, combined with the sulfur to form crystals on a scale never before seen by humans.

When Naica's ores are no longer viable, the mine is closed and the pumping is stopped, then the caves will be submerged - and the crystals will start growing again.The only reason humans can get in the caves at all is because of the ongoing pumping operations that keep them clear of water.

Flash with backlighting Picture with flash only

FOSFATOS

• Habitualmente colores claros

• Brillo no metálico

• Apatita es el más importante

APATITA Ca5(PO4)3(F,Cl,OH)

• Hexagonal

• Dureza 5

• Color verde, azulado, pardo

• Brillo vítreo a céreo

• Raya blanca

WOLFRAMATOS

WOLFRAMITA (Fe,Mn)WO4 (Monoclínico)

• Clivaje perfecto

• Muy pesado (6-7)

• Brillo resinoso

• Color pardo – negro

• Raya casi negra a parda

• Mena de wolframio: fabricación de metales duros, acero, etc.