domingo, 17 de abril de 2016

Quartz

Quartz


Amethyst

Mun. Las Vigas de Ramírez, Veracruz, Mexico
Rock Crystal

Selvino, Seriana Valley, Bergamo Province, Lombardy, Italy
Rose Quartz, etc.

Taquaral, Itinga, Jequitinhonha valley, Minas Gerais, Brazil
Smoky Quartz

Mooralla, Southern Grampians Shire, Victoria, Australia
Formula:
SiO2
System:
Trigonal
Colour:
Colorless, Purple, Rose, ...
Lustre:
Vitreous
Hardness:
7
Name:
Quartz has been known and appreciated since pre-historic times. The most ancient name known is recorded by Theophrastus in about 300-325 BCE, κρύσταλλος or kristallos. The varietal names, rock crystal and bergcrystal, preserve the ancient usage. The root words κρύοσ signifying ice cold and στέλλειυ to contract (or solidify) suggest the ancient belief that kritallos was permanently solidified ice. 

The earliest printed use of "querz" was anonymously published in 1505, but attributed to a physician in Freiberg, Germany, Ulrich Rülein von Kalbe (a.k.a. Rülein von Calw, 1527). Agricola used the spelling "quarzum" (Agricola 1530) as well as "querze", but Agricola also referred to "crystallum", "silicum", "silex", and silice". Tomkeieff (1941) suggested an etymology for quartz: "The Saxon miners called large veins - Gänge, and the small cross veins or stringers - Querklüfte. The name ore (Erz, Ertz) was applied to the metallic minerals, the gangue or to the vein material as a whole. 

In the Erzgebirge, silver ore is frequently found in small cross veins composed of silica. It may be that this ore was called by the Saxon miners 'Querkluftertz' or the cross-vein-ore. Such a clumsy word as 'Querkluftertz' could easily be condensed to 'Querertz' and then to 'Quertz', and eventually become 'Quarz' in German, 'quarzum' in Latin and 'quartz' in English." Tomkeieff (1941, q.v.) noted that "quartz", in its various spellings, was not used by other noted contemporary authors. "Quartz" was used in later literature referring to the Saxony mining district, but seldom elsewhere. 

Gradually, there were more references to quartz: E. Brown in 1685 and Johan Gottschalk Wallerius in 1747. In 1669, Nicolaus Steno (Niels Steensen) obliquely formulated the concept of the constancy of interfacial angles in the caption of an illustration of quartz crystals. He referred to them as "cristallus" and "crystallus montium". 

Tomkeieff (1941) also noted that Erasmus Bartholinus (1669) used the various spellings for "crystal" to signify other species than quartz and that crystal could refer to other "angulata corpora" (bodies with angles): "In any case in the second half of the XVIIIth century quartz became established as a name of a particular mineral and the name crystal became a generic term synonymous with the old term 'corus angulatum'."
Polymorph of:
Coesite, Cristobalite, Mogánite, Seifertite, Stishovite, Tridymite
Isostructural with:
Berlinite
Quartz is the most common mineral found on the surface of the Earth. A significant component of many igneous, metamorphic and sedimentary rocks, this natural form of silicon dioxide is found in an impressive range of varieties and colours. There are many names for different varieties: Cryptocrystalline varieties of quartz are listed separately under chalcedony, and include agate.

sábado, 16 de abril de 2016

Diamond

Diamond



Diamond

Miba Mine, Mbuji Mayi, Kasaï-Oriental, Democratic Republic of Congo
Diamond

Kimberley, Francis Baard District, Northern Cape Province, South Africa
Diamond

Kimberley, Francis Baard District, Northern Cape Province, South Africa
Formula:
C
System:
Isometric
Colour:
Colourless, yellowish to ...
Lustre:
Adamantine, Greasy
Hardness:
10
Name:
From Greek "adamas", 'invincible'. First known use by Manlius (A.D. 16) and Pliny (A.D. 100).
Polymorph of:
Chaoite, Graphite, Lonsdaleite
Diamond is the hardest natural substance known. It is formed deep in the mantle, and is only brought to the surface via kimberlite pipes, lamprophyres, eclogites and other rocks that originate deep within the mantle. It is also found in alluvial deposits, along with quartz, corundum, zircon and other minerals, derived from such rocks, and in certain meteorites.

The formation processes of the variety carbonado are unclear. 

Corundum

Corundum



Sapphire

Gem gravels, Ratnapura, Ratnapura District, Sabaragamuwa Province, Sri Lanka
Ruby

Mysore District, Karnataka, India
Ruby

Mysore District, Karnataka, India
Formula:
Al2O3
System:
Trigonal
Colour:
Colourless, blue, red, ...
Hardness:
9
Member of:
Hematite Group
Name:
Named "corinvindum" in 1725 by John Woodward and derived from the Sanskrit, kuruvinda ("Ruby"). Richard Kirwan used the current spelling "corundum" in 1794. Known by many names in ancient times: adamant, sapphire, ruby, hyacinthos, asteria, etc.
The aluminum analogue of Eskolaite, Hematite, and Karelianite.
The red (Cr-bearing) gem variety is called Ruby.
The blue (Fe- and Ti-bearing) gem variety is called Sapphire. 

Ruby

Ruby



Ruby

Mysore District, Karnataka, India
Ruby

Mysore District, Karnataka, India
Ruby

Gairo, Kilosa District, Morogoro Region, Tanzania
Ruby

Kleggåsen Ruby Quarry, Froland, Aust-Agder, Norway
Formula:
Al2O3
System:
Hexagonal
Colour:
Red
Hardness:
9
A variety of Corundum

A red, gem variety of corundum. The red colour is caused by minor amounts of trivalent Cr replacing Al in the crystal structure.

In traditional gemmological terms, ruby has to be blood-red and of clear, facetable quality to justify the name, however in wider usage any corundum with a red or reddish colour has attracted the name 'ruby', and this name is usually applied in this way by mineral collectors.

Pink corundum is usually referred to in gemmological terminology as pink sapphire rather than ruby.

Pure Cr2O3 occurs in nature as the mineral eskolaite which is green.

Emerald

Emerald



Emerald, etc.

Boyacá Department, Colombia
Emerald

Byrud Emerald Mine, Minnesund, Eidsvoll, Akershus, Norway
Emerald

Coscuez Mine, Mun. de Muzo, Vasquez-Yacopí Mining District, Boyacá Department, Colombia
System:
Hexagonal
Name:
Emerald has priority over beryl as a mineral name. Emerald was known in antiquity and was prized as a gem. In the 1790s, Louis Nicolas Vauquelin, the discoverer of chromium, demonstrated that emerald and beryl were essentially the same chemical compound and that emeralds, sensu strictu,contained chromium. Nonetheless, emerald continued to be listed as the preferred species name for many decades and emerald finally began to be used as a variety name for beryl by the 1830s. New emerald reports referring to ordinary green or even blue beryl persisted in the amateur literature into the twentieth century. In the latter twentieth century, it was discovered that some emeralds contain more vanadium than chromium.
A variety of Beryl

A green gem variety of Beryl, highly sought after as a precious gem stone. The majority of the world's gem quality Emeralds come from the Muzo area of Colombia.

The colour in Emerald is caused by trace amounts of a chromophore such as Chromium or Vanadium.