颜色丰富多彩的尖晶石刻面 Color varieties of facetted spinel	天然尖晶石晶体　Spinel Crystals

 

世界著名的尖晶石 (Spinels from various locality)
上图27.8ct　 下图146.43ct 1985年左右发现于帕米尔高原 (Discovered in 1985)(Pamir Mtns.)	32.5x31.5ｘ15.7mm　150ct 产地不明(Unknown locality)	戒面(Ring) 9.5ct MogokBurma 其他的产于斯里兰卡　1.89～46.48ct (Other stones fromSrilanka) American Museum ofNatural History	上图(top)　　　 3.74 & 1.36ct 下图(bottom)　0.99～3.74ct 产于马达加斯加 Ilakaka, Madagascar

 

因为成分和成因都很相似，世界上产出红蓝宝石的地区都有尖晶石产出。缅甸、斯里兰卡等地从古至今，都是优质尖晶石的主要产出国。
照片上大而美丽、近乎完美的尖晶石是1985年在帕米尔山脉发现的。
世界各地的博物馆中，可供参观的宝石级的尖晶石大都是产自帕米尔地区。这样的珍品产出量极为稀少，因此在市面上常见的大都是晶体标本级的。
1990年末，在马达加斯加的依拉卡卡（Ilalakaka）地区发现大量的颜色丰富的尖晶石，这里逐渐成为优质尖晶石的主要产地。

　Spinel is found as a by-product of ruby and sapphire exploitations. Burma and Srilanka always have been the major spinel producers. In 1985, gem spinel of extreme beauty and size was discovered at Pamir Mtns., which is considered as the locality of "one of the kind" museum piece spinels in the world. Such spinels are collected sporadically and most of spinels we encounter are only specimen classes. From end of 1990's, Ilalakaka alluvial deposit of Madagascar has been known as the major spinel of fantastic shades.

 

重量1.21 - 4.3ct 产自越南	最上方 12.81ct 下面的两颗分别是4.46和3.58ct 产自越南	是从一颗300克的原石上切割下来的刻面宝石 facetted stones from one 300g crystal He An, 产自越南

 

    从1980年起，越南很多地方相继发现优质的红蓝宝石，其质量不亚于缅甸和斯里兰卡。尖晶石作为其附产物也大量被发现。

　Since early 1980s, high quality ruby and sapphires, equivalent to Burmese and Srilankan one have been discovered in wide areas of Vietnam.
Spinel has been reported as bi products of ruby and sapphire mining.

 

什么是尖晶石？ （What is spinel）

尖晶石主要成分是氧化镁和氧化铝，结晶习性是等轴晶系漂亮的正八面体。
镁被铁置换就是铁尖晶石，被锌置换就是锌尖晶石，铁完全置换镁形成磁铁矿，铬置换铁尖晶石形成铬铁矿，这些类质同相的等轴晶系都是八面体结晶的尖晶石族矿物。
这些尖晶石族矿物中，镁尖晶石可以形成宝石级的透明的晶体。如果含有锌，会变成深色，不过还叫做镁尖晶石。
尖晶石产生于岩浆岩和接触变质岩中，宝石级的尖晶石大多和红蓝宝石一起产自大理岩中。
尖晶石和刚玉（红蓝宝石）如下表，在性质上很相似，颜色等都十分相似。

 

 

	化学組成 (Composition)	晶系 (Crystal System)	摩氏硬度 (Hardness)	比重 (Density)	折射率 (Refractive Index)
尖晶石 (Spinel)	MgAl2O4	等軸晶系(Cubic)	8	3.58～3.98	1.712～717
刚玉 (Corundum)	Al2O3	三方晶系(Triclinic)	9	3.99～4.05	1.757－776

 　Spinel is a compound of magnesia(MgO) and alumina(Al2O3) and is thus a magnesium aluminate(MgAl2O4), found as accessories in igneous rocks, in metamorphosed aluminous schists, in contact metamorphosed limestones and sometimes in high temperature iore veins. There are common spinel group minerals with chemical substitution between the end members ; MgAl2O4(Spinel), FeAl2O4(Hersinite), ZnAl2O4(Gahnite), MnAl2O4(Galaxite) and FeCr2O4(Chromite). Among spinel group minerals, only magnesium spinel is found as transparent gem crystals with various colors, mostly in crystalized calcite-marble metamorphosed rocks and its alluvial deposits of Burma, Srilanka, Afghanistan, Vietnam and in Tazania. Spinel and Corundum(Ruby and Sapphire) are very close in chemical compostion and occurence and often discovered in the same deposits.
 

 18世纪以前，红宝石和红色尖晶石被认为是同一种矿物。英国王室皇冠上的被称为“黑太子红宝石”的宝石实际上是一颗红色尖晶石，长时间被误认为是红宝石，这个故事被传为佳话。

尖晶石的呈色机理 (About spinel color)

尖晶石的呈色机理与红蓝宝石大体相同，化学成分和其他性质也很相似，靠肉眼来识别是不可能的，因此几世纪以来，二者一直混淆不清。不过，没有像黄色蓝宝石那样颜色的黄色尖晶石，因为使黄色蓝宝石至色的铁离子使尖晶石呈浅蓝或蓝绿色。
如果含杂质很少的话，二者都呈无色透明，但比起无色蓝宝石，无色的尖晶石更为稀少。

　Spinel is colored with similar mechanism as corundum. But yellow spinel does not exist. Iron impurity, which contribute to yellow color in corundum, is a cause of blue and blue-green in spinel.
Since chemical composition and other characteristics are similar, it is quite diffictl to identify spinel from ruby and sapphires with unaided eye, which is the main reason that both gemstones have been confused long time. Both spinel and corundum with pure composition are colorless, while colorless spinel is much rare than corundum.

 

7.3x6.2mm 1.51ct Pailin, Cambodia	Ø 6mm 0.78ct Mogok, Burma

蓝色的尖晶石（Blue spinel）

曾经认为，钴至色的蓝色尖晶石只有合成才有，但最近发现了天然的蓝色尖晶石。蓝色的至色机理是二价的钴离子和二价的铁离子构成的配位八面体对光的选择性吸收。这种蓝色通常带一点紫色。

　Cobalt colored blue spinel once existed only as synthetic type, but recently natural type is discovered. The blue and purplish blue color derives from octahedral cordination formed with di-valence cobalt and ferric ion.
 

 

    紫色的尖晶石（Violet Spinel）　

    带有灰色调的紫色系尖晶石，是铁离子的配位八面体对光的选择性吸收至色的。下面的照片是斯里兰卡产的1.92ct的蓝紫色尖晶石，在白炽灯下呈紫红色。实际上颜色发生了变化。颜色变化的原因下面会有所介绍。
 

 Purple and graysh-purple color derived from octahedral cordination of ferric ion.

 

1.30 - 1.67ct Ilakaka, Madagascar	Color change type 1.92ct 8.2x7.2mm 左　：　自然光　　右　：　白炽光 left　：　natural light　　right　：incandescent light Srilanka