Steve Paschall, age 12, of Newport News, Virginia, for his question:

How mane types of gold are found in the earth?

We frequently hear of yellow gold and red gold, white gold and gold tagged with numbers called carats. These are man made alloys of pure gold and various other metals. Gold is one of the basic chemical elements. The gold found in nature is the same as the gold contained in the various man made versions. A few natural samples are pure or almost pure gold. Most are alloyed or associated with a variety of other metals and minerals.

Here and there, natural gold occurs in skimpy, though valuable deposits. Microscopic particles also are strewn through many rocks. The total amount is estimated to be less than one millionth part of the earth's crust, plus some surprising quantities in sea water. It is mined from visible deposits and elaborate processes are used to extract fine fragments from low grade ores.

Since the end of the 15th century, all man's efforts to mine and extract gold from the earth has yielded no more than enough to stuff a cube shaped container 50 feet on a side.

The earth's atoms of gold are exactly the same as those in man made alloys such as red, yellow and white gold. Pure gold is found almost never and most natural samples are alloyed with silver. Samples of rich golden yellow contain less silver and those of pale yellow contain more.

Mast California gold is alloyed with about 10 per cent silver. It is found in chunky nuggets, fine flakes and small grains. More is found as golden threads, like lacy leaves and feathers, woven through layers of milky white quartz stone. These samples are called picture rocks. The gold in most Hungarian deposits contains 30 per cent silver. The purest natural gold contains only 0.3 per cent silver and is found in Australia.

Natural samples of reddish gold .may be alloyed with copper. Other natural gold is found in telluride rocks containing silvery white tellurium and perhaps iron, silenium and silver. Fragments of natural gold also may be found in mineral sulphides of iron, zinc and lead. When the telluride ores are mined for their major metals, the gold content is a by product. There may be enough of it to pay the cost of the whole operation.

The job of extracting microscopic gold fragments from igneous and other rocks is highly complex. Different methods use chemicals, gravity, water and smelting. These projects are worthwhile when ten tons of ore yield only an ounce of gold.

Pure gold is one of the densest metals, 19.3 times heavier than water. This is 24R, or 24 carat gold. It is too soft for everyday use so it is smelted with other metals to make stronger alloys. The silvery white gold used to set precious gems is alloyed with silver, platinum and palladium. Red gold may be alloyed with copper. The alloys are measured in 24 parts or carat units. A mixture of 18 parts of gold and six parts of other metals is 18 carat gold. It is more durable than 22 carat gold, which contains only two parts of other metals.