VOLCANIC STONE

Dominion, Volume 24, Issue 52, 25 November 1930, Page 8

VOLCANIC STONE

“Trade Demands Met” TESTS BY EXPERT \ A report upon a volcauie stone known as “vitric tuff,” which is found in the Hinuera Valley, Waikato, has been made to the Department of Industrial and Scientific Research by Dr. P. Marshall, 1 the department’s petrologist. Interest attaches to tests upon this stone, in view of the fact that work will soon be started upon the National Museum and Art Gallery in Wellington, for it is stated to meet the wants of the building trade in New Zealand, as it is soft, easy to. work and agreeable in tint, while in addition it has perfect resistance to weather action. It is readily accessible and can be quarried cheaply. Dr. Marshall states in his report that the material from which the rock is formed was thrown into the air by a violent explosive, volcanic eruption. The particles were still sufficiently hot when they fell back to the ground to fuse together partially and form a solid rock which is thus mainly composed of volcanic glass particles fitted together, though there are many crystals disseminated through it. The colour of the stone is pale yellow or a creamy tint, but is varied by the Inclusion of small fragments of white rhyolite. In some neighbouring outcrops the stone is whiter, in others yellower, while near Litchfield it has a bluish-grey tint. Tests show that this vitric tuff is stronger and less absorptive than Oatnaru stone, the well-known New Zealand building stone. The softness and easy working quality of the stone at once arouse suspicion as to its permanence. The geological evidence on this point, Dr. Marshall points out, is very strong. The outcrop of the stone marks the banks of the Waikato River when in past ages it flowed ihto the Firth of Thames. Since that time the Waikato River in its new course has worn a gorge 150 feet deep through greywacke rock. This could not have been accomplished in a less time than 10,000 years. During the whole of this vast period the face of the rock has been exposed to the sunshine, rain, and frost of the Waikato district. Its surface has worn slightly and generally evenly to what appears to be a depth of a few inches only, and there has been no decay or disintegration. No important new fractures have been developed, and the face of the rock remains in huge unbroken monoliths. Dr. Marshall adds that it. is remarkable that great use has not already been made of the stone. However, it has been used in two buildings in Auckland, and after many years it is to-day in as perfect a condition as when it was put into place.