b'Pyritethe firestoneFeatureamounts of Cu, Co, Ni function as donors of electrons in n(this diode property of natural pyrite seems to have been little type, while As is the acceptor of electrons in p type. Notestudied). In the radio circuit, virtually, only the positive part of that arsenic can be quite common in pyrite environmentsthe received alternating waveform is passed, thus achieving e.g. as paragenetic white iron pyrites Fe As S. Shuey (1975)the rectification. The crystal detector circuit extracts an audio gives a modal resistivity of 1x10-3 ohm m for n type, andfrequency (AF) signal impressed on the radio frequency (RF) 3x10-2 ohm m for p type pyrite. The n type tends to becarrier wave (now amplitude modulated, AM) picked up by more conductive, but the p type seems to be more common.the receiving aerial. This is connected to the primary of a Despite the many measurements and investigations of Halltransformer whose secondary provides input to the detector effect, Seebeck effect, chemistry, mineralogy, temperaturecircuit (Figure 9). An early 1900s radio receiver was simply an dependence, and concomitant magnetic behaviour, it doesaerial, the transformer, the pyrite detector (galena could also seem that more studies are needed to understand betterbe used), and a pair of headphones in parallel with a couple natural pyrites DC and AC electrical behaviour, especially inof capacitors. The pyrite detectors function was to pass only aggregate rather than single crystal form. the positive part of the incoming waveform and to produce a pulsating DC signal with RF and AF components. One of the It is interesting that pyrite has the useful electrical propertycapacitors was manually variable and was used to tune the (as does galena) of both p and n semiconductor typesincoming signal i.e. select the senders frequency, the other sometimes occurring in the one crystal (Shuey 1975). Thiscapacitor sent the RF component to earth thus bypassing resulted in pyrites use as a detector in early radiowave crystalthe headphones. The headphones were high impedance to set reception circuits. A cats whisker wire was used to probemaximise the voltage, and provided the listener with a sound the crystal surface until a suitable zone was encountered tosimilar to that used to modulate the carrier wave. No battery fulfil the function. A p-n junction acted as a rectifier. The por other power source was required. Sensitivity was low, but type sulphide has no conduction electrons; the n type has noadequate. All very simple and still used by hobbyists to this conduction holes. Holes and electrons cross the boundaryday. Pyrite was one of the key components in the early days making the p type more negative and the n type moreof radio transmission. Many a schoolchild made a bits and positive. The application of a potential difference opposite topieces receiver with the silver foil from a bar of chocolate, a this interface polarity, a forward bias, gives a large current,thimble, a cardboard roll, some wire and a crystal costing a but reverse bias decreases the current by orders of magnitudefew pennies.Figure 9.Communications were vital in the early days of geophysical prospecting. Here, in this depiction of a base camp, lakeside in the outback, intrepid party leader Ashley, after a bush tucker breakfast, was able to receive instructions from head office and, by rotating the tuning capacitor, could catch news broadcasts, or soothing music, before facing the rigours of the exploration day. This environmentally friendly technology depended on the pyrite detector. A yellow piece of rectifying pyrite crystal (see inset) is held in a cats whisker jig. Polluting fossil fuel power was not required. On the ground, between the bucket and the tree, is one of the instruments of the day: a dip-needle (see Heiland 1940), which, when properly compensated and oriented, indicates changes in vertical magnetic intensity along Ashleys traverse lines (note that the name Ashley is gender neutral.59 PREVIEW DECEMBER 2019'