Gold is a constituent of granite and of plutonic rocks. Such crystalline rocks may be the primal source of the gold, which is concentrated in veins(1).
Has granite have gold in it?
Accordingly to a recent paper by Prof. George P. Merrill, Curator of the Department of Geology of the U. S. National Museum, Washington, upon “An Occurrence of Free Gold in Granite”, describes an interesting instance of the dissemination of this noble metal in the substance of granite of normal composition believed to be from Sonora, Mexico.
Professor George P. Merril submitted a number of thin sections of the rock to examination and with the aid of the microscope gave confirmatory evidence.
The goelogist, found the “gold in small scales, rarely exceeding a millimeter in diameter, distributed through the scales of mica and apparently enclosed in both the feldspar and quartz granules.”
So, how can you tell if a rock has gold in it?
To identify gold inside of a piece of quartz, hold a magnet against the rock. If the quartz sticks to the magnet, then it contains iron pyrite, or fool’s gold.
You can also try to scratch a piece of glass or unglazed ceramic with the gold portion of the rock. Real gold will not scratch these substances.
What Is Fool's Gold?
“Fool’s gold” is a common nickname for pyrite* — as geology.com describes.
Pyrite received that nickname because it is worth virtually nothing, but has an appearance that “fools” people into believing that it is gold.
The nickname “fool’s gold” has long been used by gold buyers and prospectors, who were amused by excited people who thought they had found gold.
*Pyrite is a brass-yellow mineral with a bright metallic luster.
How to identify Fool's Gold?
These people did not know how to tell the difference between pyrite and gold, and their ignorance caused them to look foolish.
With a little practice, there are many easy tests that anyone can use to quickly tell the difference between pyrite and gold.
There are a few simple tests that almost anyone can use to tell the difference between pyrite and gold.
They can usually be done successfully by inexperienced people. However, wise people obtain a couple small pieces of pyrite and a couple small pieces of gold and use them to gain valuable experience.
There’s a story about gold in the mountain of Castro de Arados where Alpendorada granite is extracted.
The legend says that there was a plough of gold buried in the mountain, for those o dare to do such thing. No one ever found gold in Alpendorada granite. Till now…