Lapis lazuli
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"Lapis" redirects here. For other uses, see Lapis (disambiguation).
| Lapis lazuli | |
|---|---|
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| General | |
| Category | Rock |
| Chemical formula | (Na,Ca)8(AlSiO4)6(S,SO4,Cl)1-2 |
| Identification | |
| Color | Blue, mottled with white calcite and brassy pyrite |
| Crystal habit | Compact, massive |
| Crystal system | None, as lapis is a rock. Lazurite, the main constituent, frequently occurs as dodecahedra |
| Cleavage | None |
| Fracture | Uneven-Conciodal |
| Mohs Scale hardness | 5 - 5.5 |
| Luster | Vitreous to greasy |
| Refractive index | 1.5 |
| Streak | light blue |
| Specific gravity | 4.4 |
| Other Characteristics | The variations in composition cause a wide variation in the above values. |
Lapis lazuli, also known as just lapis, is a stone with one of the longest traditions of being considered a gem, with a history stretching back to 5000 BC. Deep blue in color and opaque, this gemstone was highly prized by the pharaohs of ancient Egypt, as can be seen by its prominent use in many of the treasures recovered from pharaonic tombs. It is still extremely popular today.
Lapis is a rock and not a mineral because it is made up from various other minerals. To be a true mineral it would have one constituent only.
The first part of the name is the Latin lapis, meaning stone. The second part, lazuli, is the genitive form of the medieval Latin lazulum, which came from Arabic (al-)lazward, which came from Persian لاژورد lāzhward. This was originally a place-name, but soon came to mean blue because of its association with the stone. English azure, Spanish azul, Italian azzurro also derives from this source. Taken as a whole, lapis lazuli means stone of azure.
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[edit] Description
The main component of lapis lazuli is lazurite (25% to 40%), a feldspathoid silicate mineral composed of sodium, aluminium, silicon, oxygen, sulfur, and chlorine. Most lapis also contains calcite (white), sodalite (blue) and pyrite (yellow). Other possible constituents are augite, diopside, enstatite, mica, hauynite, hornblende and nosean. Lazurite's formula is (Na,Ca)8(AlSiO4)6(S,SO4,Cl)1-2 [1].
Lapis lazuli usually occurs in crystalline limestones as a result of contact metamorphism.
The finest color is intense blue, lightly dusted with small flecks of golden pyrite. There should be no white calcite veins and the pyrite inclusions should be small. Stones that contain too much calcite or pyrite are not as valuable. Patches of pyrite are an important help in identifying the stone as genuine and do not detract from its value. Often, inferior lapis is dyed to improve its color, but these are often a very dark blue with a noticeable grey cast.
[edit] Sources
The finest lapis comes from the Badakshan area of Afghanistan. This source of lapis may be the oldest continually worked set of mines in the world, the same mines operating today having supplied the lapis of the pharaohs. Using this ancient source, the Indus Valley Civilization's artists used to make beautiful carvings and traders used to trade them to distant places. More recently, during the 1980s conflict with the USSR, Afghanistan resistance fighters disassembled unexploded Soviet landmines and ordnance and used the scavenged explosive to help mine lapis to further fund their resistance efforts.
In addition to the Afghan deposits, lapis has been found in the Andes near Ovalle, Chile, where it is usually pale rather than deep blue. Other less important sources are the Lake Baikal region of Russia, Siberia, Angola, Burma, Pakistan, USA (California and Colorado) and Canada.
[edit] Uses
Lapis takes an excellent polish and has been made into jewelry, carvings, boxes, mosaics, ornaments and vases. In architecture it has been used for cladding the walls and columns of palaces and churches.
It was also ground and processed to make the pigment Ultramarine for tempera paint and, more rarely, oil paint. Its usage as a pigment in oil paint ended in the early 19th century as a chemically identical synthetic variety, often called French Ultramarine, became available.
[edit] Enhancements
The most common enhancement for lapis lazuli is dyeing (staining), where a stone with white calcite inclusions is stained blue to improve the colour. Other enhancements commonly seen are waxing and resin impregnations, again to improve colour. The colour of stained lapis is unstable and will fade with time.
[edit] Imitations
Sintered synthetic blue spinel was once used as an imitation of lapis lazuli but is rarely seen today. So-called synthetic lapis lazuli (such as the Gilson product) is more properly termed an imitation, since it does not match exactly the structure and properties of the natural. It is found in various forms, complete with pyrite specks (but all lacking calcite). Various forms of glass and plastic are also commonly seen as imitations.
[edit] Cultural and historical/mythical usage
In ancient times, lapis lazuli was known as sapphire, which is the name that is used today for the blue corundum variety sapphire. It appears to have been the sapphire of ancient writers because Pliny refers to sapphirus as a stone sprinkled with specks of gold. A similar reference can be found in the Hebrew Bible in Job 28:6.
In ancient Egypt lapis lazuli was a favorite stone for amulets and ornaments such as scarabs; it was also used by the Assyrians and Babylonians for seals. Egyptian burial sites dating before 3000 B.C. contained thousands of jewelry items, many of lapis. Powdered lapis was used by Egyptian ladies as a cosmetic eye shadow.
As inscribed in the 140th chapter of the Egyptian Book of the Dead, lapis lazuli, in the shape of an eye set in gold, was considered an amulet of great power. On the last day of the month, an offering was made before this symbolic eye, for it was believed that, on that day, the supreme being placed such an image on his head.
The ancient royal Sumerian tombs of Ur, located near the Euphrates River in lower Iraq, contained more than 6000 beautifully executed lapis lazuli statuettes of birds, deer, and rodents as well as dishes, beads, and cylinder seals. These carved artifacts undoubtedly came from material mined in Badakhshan in northern Afghanistan. The word lazuli itself originates from the Persian dialect of Badakhshan. Much Sumerian and Akkadian poetry makes reference to lapis lazuli as a gem befitting royal splendor.
The Romans believed that lapis was a powerful aphrodisiac. In the Middle Ages, it was thought to keep the limbs healthy, and free the soul from error, envy and fear.
It was once believed that lapis had medicinal properties. It was ground down, mixed with milk and applied as a dressing for boils and ulcers.
Many of the blues in painting from medieval Illuminated manuscripts to Renaissance panels were derived from lapis lazuli. Ground to a powder and processed to remove impurities and isolate the component lazurite, it forms the pigment ultramarine. This clear, bright blue, which was one of the few available to painters before the 19th century, cost a princely sum. As tempera painting was superseded by the advent of oil paint in the Renaissance, painters found that the brilliance of ultramarine was greatly diminished when it was ground in oil and this, along with its cost, led to a steady decline in usage. Since the synthetic version of ultramarine was discovered in the 19th century (along with other 19th century blues, such as cobalt blue), production and use of the natural variety has almost ceased, though several pigment companies still produce it and some painters are still attracted to its brilliance and its romantic history.
[edit] Poetry
Lapis Lazuli is a poem written by William Butler Yeats. Text available at Readprint.com
As noted above, lapis lazuli is also repeatedly mentioned in the Sumerian and Akkadian Epic of Gilgamesh. For instance, the Bull of Heaven's horns are composed of Lapis lazuli.
Lapis Lazuli is also mentioned in Browning's 'The Bishop Order's His Tomb at Saint Praxed's Church'.
Finally, lapis lazuli also makes an appearance in Marianne Moore's poem, "A Talisman" - which is quoted by T. S. Eliot in his "Introduction to Selected Poems [of Marianne Moore]." The stanza of Moore's poem reads: "Of lapis-lazuli,/A scarab of the sea,/With wings spread-". Eliot, in the next paragraph, raises the question: "I cannot see what a bird carved of lapis-lazuli should be doing with coral feet; but even here the cadence, the use of rhyme, and a certain authoritativeness of manner distinguish the poem."
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