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History of Technology in India, Vol. I: From Antiquity to c. 1200 A.D. v1.c17.s3.t1: Gem Minerals Containing Beryllium

History of Technology in India, Vol. I: From Antiquity to c. 1200 A.D. v1.c17.s3.t1

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Gem Minerals Containing Beryllium

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We would now discuss the family of gem minerals containing beryllium, variously coloured, specially green and blue, and having similar hardness. In terms of chemical composition, a sharp distinction has to be made between chrysoberyl (hardness 8 1/2) BeAl2O4, a mixed oxide, and beryl (hardness 7 3/4) Be3Al2Si6O18 a cyclo-silicate. The difference in their hardness could be easily tested using another gem, topaz having an intermediate hardness of eight. In absolutely pure form, both chrysoberyl and beryl are colourless. Their colours in the gem form arise on account of lattice substitutions by other elements as specified in Table 4.

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Due to chromium and iron, chrysoberyl samples assume green and yellow colour respectively, the more usual green colour often merging into golden yellow. Milky white or greenish white cloudy chrysoberyl samples (not the clear and transparent ones) exhibit chatoyancy. Extending across the curved surface of such stones is a silvery line or streak of light, when viewed in a strong light. These samples are called chrysoberyl or oriental cat’s eye. The phenomenon of chatoyancy is due to the existence in immense numbers of microscopically small cavities arranged in a particular direction or a bundle of microscopic channels running parallel to a single direction. When viewed at right angles to this direction, a band of light is visible Table 4 — Gem Categories Of Importance In The Ancient World

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| Name English/Sanskrit | Colour | Hardness (Moh's Scale) | Reasons for non-white colour |
| Diamond/*Vajra* | usually colourless | 10 | Blue due to boron, yellow/green due to nitrogen |
| Corundum/*Kuruvinda* | “ | 9 | Pure Al₂O₃ is colourless |
| Ruby *Padmarāga* | red | 9 | Cr³⁺ replaces Al³⁺. Transition involving ligand field effect |
| Sapphire *Indranīla* | blue | 9 | Four different mechanisms including charge transfer, combination of Fe and Ti |
| Non-blue Sapphire | | 9 | Orange |
| Chrysoberyl/Cat’s eye *Marjaraksaka/Lasunia* | Green/Yellow | 8¹/₂ | Green due to Cr and yellow due to Fe substituting in Be Al₂O₄ structure. |
| Spinel/Balas-ruby/ *Bālasūryaka* | rose-red | 8 | Pure spinel Mg Al₂O₄ is colourless. Cr³⁺ substitution makes it rose-red. Fe and Mg may further alter the colour. |
| Topaz/*Pusparāga* | Yellow | 8 | Pure topaz is colourless [Al (F,OH)]₂ SiO₄. Yellow colour is due to impurities - ferrous oxide lime and alkali. Dichromic also blue |
| Beryl/*Vaidūrya* | Faint green water colour | 7³/₄ | Pure beryl Be3 Al₂ Si₆O₁₈ is colourless. Faint green due to substituting Cr³⁺. This is allochromatic effect - transition involving ligand field. |
| Emerald/*Marakata Pānnā* | Deep grass green | 7³/₄ | This is beryl containing more Cr³⁺ imparting green colour. Dichroic, the second blueish colour is due to iron. |
| Aquamarine/*Pāribhadra* | Faint blue to bluish green | 7³/₄ | Bluish tinge due to iron |

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| Name English/Sanskrit | Colour | Hardness (Moh's Scale) | Reasons for non-white colour |
| Zircon/*Gomed* | Cow-flesh colour | 7 1/2 | Pure zircon ZrSiO4 is colourless. Reddish-yellow colour of Hyacinth is due to Fe3+ decolourised on reduction to Fe2+ |
| Garnet/*Tāmrya* or *Tāmḍi* | Various colours | 7 1/4 | Family of minerals M2+3 M3+2. (SiO4)3 . Colour depends upon chemical composition. Hessonite is confused with Hyacinth. Colour due to iron. |
| Tourmaline/*Vaikrāntā* | Various colours | 7 1/4 | H9 Al3 (B.OH)2 Si4O19 pure tourmaline is light coloured. Fe2+ and Cr3+ make it dark green, Mg makes it brown and Mn dark red. |
| Quartz/*Sphaṭika* | Colourless | 7 | Pure SiO2 is colourless. Yellow citrine due to iron green chrysoprase due to nickel, violet amethyst due to manganese etc. |
| Agate/*Akik* | Light colour | 6 1/2 | Hydrated SiO2 is colourless Hydrated ferric oxide as impurity makes it brown or yellow. |
| Carnelian/*Rudhirakhya* | Red | | Heating causes dehydration and ferric oxide gives red colour to carnelian. |
| Olivine/Chrysolite/Peridot *Puttika/Jabarjad* | Bottle green | 6 1/2 | Pure Mg2SiO4 is colourless Replacement of part of MgO by ferrous oxide makes it yellowish green. Mn2+..N i2+ further change the colour. |
| Orthoclase/Feldspar Moonstone/*Candrakāntā* Sunstone/*Sūryakāntā* | Opalescent play of colour | 6 | Interference of light from thin layers. |
| Jade/*Pīlu* | White green black | 5 1/2 - 7 | Green due to Mn and Cr and Fe2+. Black due to Fe3+ |

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| Name English/Sanskrit | Colour | Hardness (Moh's Scale) | Reasons for non-white colour |
| Turquoise | Blue | | The mineral is derivative for ortho- phosphoric acid, the hydrogen atoms replaced by radicals such as Al(OH)2 Fe(OH)2 (providing green tinge) and Cu(OH), providing intense blue colour. |
| Lapis Lazuli/Ultra-marine/ *Rajāvārtal Lajhward* | Deep azure blue | 5¹/₂ | The constituent minerals are Sodium-Calcium-Aluminium silicates with sulphate and polysulphide (S⁻3) anions. The 19 outer electrons of S⁻3 unit undergo transitions within the molecular orbitals. These produce absorption band in the yellow range and hence intense blue colour. Less sulphur in the mineral system gives green colour which makes the gem less worthy. |
| Pearl/*Mukta* | Usually white | 3-4 | Iron, manganese etc.possibly complexed with organic matter, so that the colour is perishable on heat. |
| Coral/*Pravāla/Vidruma* | red,black etc. | 3-4 | “ |

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running across this bundle. The stone is usually cut along this direction so that maximum number of light-reflecting cavities are close to or on the surface, producing maximum chatoyancy. Quartz cat’s eye samples (hardness 7) show similar chatoyancy or a wave of milky light reflected from the surface, the effect in this case arising due to the presence of large number of fibres of asbestos aligned in a specific direction.

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Beryl, *vaidūrya* in Sanskrit, has a hardness (7³/₄) different from those of chrysoberyl (8¹/₂) and quartz (7), and the modern literature does not indicate that chatoyancy is observed in any beryl sample. However, green chrysoberyl sometimes looks like green beryl, and since the former gem exhibits chatoyancy effect occasionally, the Indian word *vaidūrya* has in some instances been used (unfortunately) to indicate cat’s eye gem also. Buddhabhaṭṭa’s writing (Ratnaparīkṣā or RP 200) created this confusion for the first time.

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Pāṇini referred to vaidūrya coming from Vidura. Later Patañjali, the commentator of Aṣṭādhyāyī, explained that the gem actually came from the Valavaya mountains, and was only processed in the town of Vidūra (which must have been located somewhere in South India). Centuries later, Buddhabhaṭṭa wrote about Kongavalikasimanta near the Vidūra mountain as the source of beryl or Vaidūrya (RP 199).

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Sarma (1984: 68) opined that the etymological link between Vidura and vaidūrya was ‘a fiction invented by the grammarians’, but we do not agree with him, since Patañjali’s explanation and Buddhabhaṭṭa’s corroboration have been clear enough; Patañjali’s Valavaya (mountain) is similar to Buddhabhaṭṭa’s Valikā. It is well-known that Konga kingdom once governed the beryl mine of Coimbatore of the Salem district from which beryl gems were supplied to the Romans.

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Alfred Master has suggested (1943-46) that the veluriya, the Pali word, was actually a Dravidian word preceding Pāṇini’s vaidūrya, and both were the adjectival forms of Velur (or modern Belur), which is in the heart of the beryl mines of Coimbatore. The 500 A.D. inscription of the Ganga king Durvinita mentions both Velur as well as the Punnata kingdom described by Ptolemy as ‘Punnata in which is the beryl’. Velur might have been known to Panini as Vidur (‘the far away city’) where the beryl gem from the nearby mountains were processed.

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Thus, the identity of vaidūrya with beryl is well- established. It was known to be quite different from cat’s eye. Kauṭilya listed beryl vaidūrya and cat’s eye mārjārakṣaka as distinctly separate gem (AS2.11.30 and 39).

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Kauṭilya never mentioned marakata (emerald, the darker green variety of vaidūrya or beryl) which used to be imported to India from Egypt probably after his era. In the post-Christian era, we find vaidūrya and marakata being mentioned together to mean the same family of green gem.

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