Alexandrite flashing green and red: A brand new chapter or Lankan gems | Sunday Observer

Alexandrite flashing green and red: A brand new chapter or Lankan gems

Alexander the Great was once gifted a gem, which he had never seen before. The precious stone took a greenish colour, and proving how much he loved the gem he wanted to look at it again before going to bed, the same day.

Surprisingly, it wasn’t the stone he checked during the day. Instead of the green colour the stone flashed a reddish tint. Alexander’s immediate thought was that he had been cheated by the servant who brought it to him, so that he commanded his assassination. However, he later learnt, the stone he was gifted with was a wonder of nature, where it takes green colour in day light and red at night. Ultimately, the particular gem was named after the Great Alexander, and came to be known as Alexandrite.

This is not a story about Alexander the Great, but about alexandrite. Sri Lanka has one of the best alexandrites in the world, producing both alexandrite and cat’s eye, both species falling under the category of chrysoberyl. These gems command a higher value in the international gem market due to their colour, quality, chatoyancy and size. In all these features they are superior to those found in Brazil, Russia and Myanmar, the global competitors for Sri Lankan gems.

 

However, the story is about an unusual source or rather a deposit of alexandrite found in Sri Lanka. Even though the Sri Lankan gem industry relies on gravel layers (illam) this particular gem, the alexandrite deposit is located in hard rock. In other words it is not in a gravel base but a rock base which makes it easier in finding gems.

Dr Chandawimal Siriwardana, a veteran Geologist and Director General of the Geological Survey and Mines Bureau of Sri Lanka told the Sunday Observer about this gem deposit and its significance, which he had extensively researched on.

“As shown in historic records, the Yakkalamulla chrysoberyl deposit had been discovered in the early 1900. The location had been kept secret by the owners of the land to ensure that no outsider would encroach the property. Without having carried out any excavation for several decades, prospecting recommenced in 1982.

According to the locals, gem mining had been carried out at that time in the marshy land, approximately 50 m north of the current mining site which was seasonally used for paddy cultivation” said Dr. Siriwardana.

In the past, Galle and Matara districts had been famous for alexandrites and zircons (Matara Diamonds). While most of the gem beds were prospected around Morawaka, Rakwana and Bulutota massifs, Tawalama, Dikkumbura and Neluwa in south west Sri Lanka, chrysoberyls have been sited in abundance in locations such as Yakkalamulla and Morawaka.

However, according to Dr. Siriwardana, these source rocks have hardly been prospected.

“Some chrysoberyls and cat’s eye had been recovered from these paddy fields but most of the stones were fractured.

Recently, a gem miner discovered some green lustrous stones while clearing the out flow canal of his paddy field. Consequently, mass scale mining was carried out in the adjacent gravel bed by gem prospectors who found the gem gravel layer extending to the weathered pegmatitic rock” he described.

The Yakkalamulla deposit is about 150 km off Colombo near Deniyaya in the Galle district. It is positioned at the bottom of a valley, extending to a marshy head stream of a drainage tributary of the Nilwala Ganga.

These stream beds are identified as the best prospecting sites with good gem deposits.

Chrysoberyls from the Yakkalamulla deposit show colour change effects as follows: under fluorescent light similar to daylight the stones appear green and under tungsten lamplight they take on a reddish tint. This effect is shown in some cat’s eye stones as well.

So far, the vertical mine shaft in Yakkalamulla has reached a depth of 18 m approximately, and the deposit has produced substantial quantities of valuable alexandrite and cat’s eye varieties.

The Yakkalamulla gem deposit cannot be forgotten as a single incident. It could be a discovery of a series of such gem reserves. Dr. Siriwardana believes, there is a great likelihood of locating similar gem deposits in this geological setting. “But it has to be uncovered by conducting a detailed geological exploration.

Along with this deposit, all such resources could provide additional high quality chrysoberyls for the future gem market” he said.

If the Government focuses on this prospected gem reserves, it could be the beginning of a brand-new chapter for the Sri Lankan gem industry where the country can assure a continuous supply of pure gems to the international market. 

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