INTRODUCTION
Vitrified stones are simply stones that have been melted to a point where they form a glass or glaze. There is much debate in archaeological circles over the ancient examples under study for two reasons. Firstly, few cases are known to have been tested and even if they have, there are many questions over how they were made.
Glassy rocks form naturally under conditions of high temperature and pressures found in and around volcanoes. Glass or glazes are traditionally created using a furnace. Furnace or kiln examples are found on everyday objects such as glassware and ceramics. The ceramics glazes are created by pasting certain finely crushed stones, sometimes with tinctures, onto fired pots and plates. The whole is then fired to temperatures usually in excess of 1000 degrees centigrade.
The difficulty with many of the curious ancient vitrified examples is that they are found on objects so large that they cannot be placed in a furnace. The vitrification process itself is quite a mystery. A team of chemists on Arthur C. Clarke’s Mysterious World subjected rock samples from 11 forts to rigorous chemical analysis. They concluded that the temperatures needed to produce the vitrification were up to 1,100°C. Simply burning the walls with wood interlaced with stone could not achieve such temperatures. Recent experiments along these lines have had virtually no success at all.
There are several confirmed cases of unusual vitrified remnants from across the globe. In Europe, there are several forts and buildings with vitrified ramparts. The crude stone enclosure walls seem to have been subjected to the action of heat. No mortar has been found in any of these structures. Despite this, the rocks seem to be fused together.
This fusion is uneven throughout the various forts and even in a single wall. Some stones are only partially melted and calcined. Whilst in others their adjoining edges are fused firmly together. In many instances, pieces of rock are enveloped in a glassy enamel-like coating, which binds them into a whole. At times, the entire length of the wall presents one solid mass of vitreous substance.
It is not clear why or how the walls were vitrified. Some have argued that it was done to strengthen the wall, but the heating weakens the structure. Battle damage, as some have proposed, is unlikely to be the cause. The walls would need carefully maintained fires to ensure vitrification.
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