In the investment world, we’ve all heard the best bet is to put your money in gold. When all the other major commodities, such as oil and precious metals, are experiencing a decline in prices, gold always seems to be on the up and up.But why is gold so stable? And why is it able to serve as a monetary benchmark?Much of the reason gold’s value is ever increasing is the way it is stored. Unlike other precious metals, such as copper, once gold is mined, it’s most often stored as bullion or as jewellery. Even the small amount of gold used in electronics is usually recycled. So most of the gold that’s ever been mined is still around in one form or another.Having most of the world’s gold stored in various forms differentiates it from other commodities.Let’s take a look at copper, which is another precious metal that’s fetching higher prices on the exchanges these days. In 2010, miners produced 16.2 million tonnes, whereas the amount of copper held in inventories around the world at the time was only around 645,000 tonnes. The annually produced copper greatly outweighs the copper held in inventories because the resource is almost immediately used for various purposes.If all the mining companies stopped producing copper, we’d have major problems. The inverse is true with gold. In the same year, only around 72 million troy ounces were produced while 5 billion ounces sit in reserves. If all the gold production came to a screeching halt, it wouldn’t really be a big deal because the amount produced annually is only about 1.4 per cent of the world’s inventory.So while other commodity prices are more contingent upon the changes in production (more or less is discovered and mined), gold values are more impacted by sentiment or demand. And during tough financial times such the 2008 global meltdown, the demand for gold skyrocketed, sending the price for gold soaring as well.In addition to having most of the mined gold sitting in physical forms, the value of gold is also not tied to any other commodities. For example, oil prices per barrel, which is extremely volatile for all its sharp spikes and valleys, are often tied to the value of other commodities. The same isn’t true for gold, which functions more like a currency than a commodity.All that glittersWhile gold prices have been historically stable and have continued to progressively increase over the past couple of decades, some analysts in financial circles caution that gold won’t always be so stable. After all, what goes up must eventually come down.Compare the prices through the decades. In 1970, the price of gold was just $37 per troy ounce. Cut to today, and the current price is $1,600.85. The price has steadily increased since the mid-1980s, but as the economic recovery in North America marches forward, the prices are slowly coming down from an all-time high of $1,900 per troy ounce.While the price of gold is still up by 5 per cent compared to last year, assuming the economic recovery continues in the U.S., it’s likely the price will continue to slowly creep downward.However, with all factors considered, gold is still the most stable and least volatile commodity to consider for a long-term investment.