Samples of synthetic, ultrafine-grained quartzite were prepared by hot-pressing aggregates of crushed, clear Brazilian quartz of mean grain size 0.4 mm at 300 MPa and 1373 and 1473 K. The samples displayed rapid grain-growth to ca. 12–20 mm with ,2% porosity at 1473 K, facilitated by the 0.6 wt% of water adsorbed onto the grain boundaries during sample preparation. This water could be driven off by preheating, thereby preventing grain-growth. Sufficient water was incorporated during growth into the coarsened samples to render them weak and ductile. These were deformed experimentally in the b-quartz field using an argon gas medium apparatus at 300 MPa confining pressure at temperatures mainly between T ¼ 1273 and 1473 K. Ductile flow was described by the flow law

with stress, s, in MPa, and grain size, d, in microns and strain rate e_ in s21. R is the gas constant and f(H2O) is water fugacity. Based on observation of grain flattening, optical strain features, shapes and densities of dislocation arrays, and flow law parameters, samples deformed dominantly by dislocation creep, with some contribution from grain-boundary sliding. Bearing in mind possible changes in the flow law parameters over the extrapolation interval and possible effects of the a–b phase transition, extrapolation to natural strain rates and temperatures predicts plastic flow at higher flow stresses at the same water fugacity at greenschist facies temperatures than previously published flow laws.

The early advances in understanding the internal structure of the Earth and the nature of earthquakes were achieved with a very limited number of seismic stations. Yet, by 1914, not only the presence of a core was recognised by Oldham (1906) from his analysis of the travel times of seismic waves from 14 earthquakes across the globe, but also a good estimate of its radius had been made (Gutenberg, 1913).

Availability of energy is key to wealth, political and military power, and living standards. Energy availability and consumption may be the most reliable measure of an economy. There is a direct relationship between energy consumption and countries’ gross domestic product (GDP) and the Human Development Index (HDI). Energy security, which is the relative certainty that energy supplies for a country will be available, constitutes a primary security concern for countries with high energy demands and countries with increasing energy use. Even though there appears to be no immediate shortage of hydrocarbons, this non-renewable resource is being supplemented by renewable energy. The Renewable Energy Era has already begun. Reduction in CO2 emissions is underway because of government regulations and market forces. A completely renewable energy future may be in ourfuture, but its timing is very uncertain as renewable energy presently contributes less than 10% of energy, and that supply is highly concentrated geographically. The potentially largest natural gas resource remaining on Earth, oceanic natural gas hydrate (NGH), may substantially supplement the natural gas supply far into the future. An additional benefit is that natural gas produces less CO2 per Btu and also has a much lower pollution potential than any other combustion fuel. Natural gas is the clean hydrocarbon fuel that will reach into the renewable energy future. Its continued availability at affordable prices becomes increasingly important as coal and oil power plants are retired and energy demand becomes increasingly filled by development of renewable or intermittent power sources.

The successful exploration geologist uses knowledge of geologic relationships and ore-deposit styles, tempered by experience, to interpret all information available from a given prospect in order to develop an understanding of its mineral potential. In the case of exploration for epithermal gold deposits, this understanding can be augmented by familiarity with active hydrothermal systems, their present-day analogues.