Juni 2012 - Jejaring Kimia


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Juni 03, 2012

CHALCOPYRITE [Copper Iron Sulfide]

Juni 03, 2012 5

CuFeS2, copper iron Sulfide [Major ore of copper]
Chalcopyrite (or copper pyrite), looks like, and is easily confused with pyrite, FeS2. Chalcopyrite is one of the minerals refered to as "Fool’s Gold" because of its bright golden colour. But real gold is a more buttery yellow and is ductile and malleable.
As an ore od copper, the yield of chalcopyrite is rather low in terms of atoms per molecule. It is only 25%, compared to other copper minerals such as chalcocite, Cu2S - 67%; cuprite, Cu2O - 67%; covellite, CuS - 50% or bornite Cu5FeS4 - 50%. However the large quantities and widespread distribution of chalcopyrite make it the leading source of copper. Chalcopyrite is a common mineral and is found in almost all sulfide deposits. Fine crystals of chalcopyrite have a unique character and can add to anyone’s collection.

Physical Characteristics

Colour : brassy yellow, tarnishes to irredescent blues, greens, yellows and purples
Luster : metallic
Transparency : Crystals are opaque
Crystal System : tetragonal; bar 4 2m
Crystal Habits : predominantly the disphenoid which is like two opposing wedges and resembles a tetrahedron. Crystals sometines twinned. Also commonly massive, and sometimes botryoidal
Cleavage : rather poor in one direction
Fracture : conchoidal and brittle
Hardness : 3.5 - 4
Specific Gravity : approx. 4.2 (average for metallic minerals)
Streak : dark green
Other : Some striations on most crystal faces
Associated Minerals : quartz, fluorite, barite, dolomite, calcite, pentlandite, pyrite and other sulfides
Major Occurrences : include Chile, Peru, Mexico, Europe, South Africa, several USA sites and many others around the world
Best Indicators : crystal habit, tarnish, softness and brittleness
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Rino Safrizal
Jejaring Kimia Updated at: Juni 03, 2012

Juni 01, 2012

SPODUMENE [Lithium Aluminium Silicate]

Juni 01, 2012 0
[ Silicates : Inosilicates : Pyroxenes ] LiAlSi2O6, lithium aluminium Silicate

Spodumene is a rock forming mineral in granites and pegmatites that bear other lithium minerals. Spodumene is a relatively new mineral to science, being discovered in the last three centuries and gem varieties have only been discovered in the last 120 years. Transparent deeply coloured spodumene has two varieties called kunzite and hiddenite. Kunzite is the more common of the two and is known by most gemstone collectors and fanciers. It is a lovely pink to lilac colour that is unique in the gem kingdom. Hiddenite comes North Carolina and is not well known or abundant. It has an usual green colour that is unlike either peridot or emerald. Spodumene is strongly pleochroic and therefore a gem cutter must take care to orient the stone in the best position for the deepest colour. Spodumene's cleavage, parting and fracture also make it a challenge for any gem cutter.

Physical Characteristics

Colour : white, colourless, gray, pink, lilac, violet, yellow and green
Luster : vitreous
Transparency : crystals are transparent to translucent
Crystal System : monoclinic; 2/m
Crystal Habits :
include prismatic, generally flattened and elongated crystals. The termination is usually the two faces of a dome or rounded, curved and faces indisernable. Crystal faces are often pitted and rough. Some crystals of spodumene have been found in record large crystals of more than 12 meters long
Cleavage :
perfect in two direction at close to right angles and a parting direction that breaks diagonally transect one of the cleavage angles and is parallel to the typical flattening of the crystals

Fracture : splintery due to the cleavage and parting
Hardness : 6.5 - 7
Specific Gravity : approxi. 3.2 (slightly above average)
Streak : white
Other :
index of refraction is 1.66, prism faces are deeply striated lengthwise and clear colourful varieties show strong pleochroic colour intensity variation when a crystal is viewed from the top or bottom then from other directions
Associated Minerals : lepidolite, plagioclase feldspars, quartz, tourmaline and topaz
Major Occurrences :
include California, North Carolina and South Dakota, USA; Afganistan; Pakistan; Brazil and Madagascar
Best Indicators : crystal habit, striated prisms, colour, fracture and cleavage
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Rino Safrizal
Jejaring Kimia Updated at: Juni 01, 2012

LEPIDOLITE [Potassium Lithium Aluminium Silicate Hydroxide Fluoride]

Juni 01, 2012 0
[ Silicates : Phyllosilicates : Micas ]

KLi2Al(Al, Si)3O10(F, OH)2, potassium lithium aluminium Silicate Hydroxide Fluoride

Ore of lithium, ornamental stone and heat insulator for industrial purposes
Lepidolite is an uncommon mica and has only in the past decade become available on the mineral market in large quantities. Lepidolite is an ore of lithium and forms in granitic masses that contain a substantial amount of lithium. The lithium content in lepidolite does vary greatly however and low lithium lepidolite is nearly useless as an ore of lithium. The typical violet to pink colour of lepidolite is characteristic and is the only field test available to identify lepidolite from other micas. Pink muscovite or very pale lepidolite may confuse an identification.

Lepidolite, like other micas, has a layered structure of lithium aluminium silicate sheets weakly bonded together by layers of potassium ions. These potassium ion layers produce the perfect cleavage. Lepidolite crystals accompany such other lithium bearing minerals such as tourmaline, amblygonite and spodumene and can add greatly to the value of these specimens. A rock made of granular pink lepidolite and red to pink tourmaline is used as an ornamental stone for carving. Single large plates or "books" of lepidolite can have appealling violet colour and make attractive mineral specimens.

Physical Characteristics

Colour : violet to pale pink or white and rarely gray or yellow
Luster : vitreous to pearly
Transparency : crystals are transparent to translucent
Crystal Habits :
Include tabular to prismatic crystals with a prominant pinacoid termination. Lepidolite's four prism faces and two pinacoid faces form pseudo-hexagonal crystal "books". The sides of the crystal often tend to tapper. Also as micaseous, lamellar or granular rock forming masses
Cleavage : perfect in one direction producing thin sheets or flakes
Fracture : not readily observed due to cleavage but is uneven
Hardness : 2.5
Specific Gravity : approx. 2.8+ (average)
Streak : white
Other :
sheets are flexible and elastic, meaning they can be bent and will flex back to original shape. Also some specimens may show triboluminescence
Associated Minerals :
quartz, feldspars, spodumene, ambygonite and tourmaline especially elbaite
Major Occurrences :
include Brazil; Ural Mountains, Russia; several African localities and California, USA
Best Indicators :
crystal habit, colour, cleavage, elastic sheets and associations
Read More
Rino Safrizal
Jejaring Kimia Updated at: Juni 01, 2012

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