Placer gold is a form of gold recovered from loose deposits of sand, gravel, and sediment, having been liberated from its original hard-rock source by weathering and then transported and concentrated by water. This process of detachment and movement by natural forces causes the gold particles to accumulate in riverbeds, floodplains, and ancient stream channels. Placer gold is fundamentally different from the “lode” gold still trapped within solid rock veins, presenting unique characteristics that allow for its separation from ordinary earth materials. This guide will clarify the specific traits, common shapes, and reliable field tests that distinguish genuine placer gold from its common visual mimics.
The Defining Physical Traits
The most striking trait of gold is its color, which presents as a rich, deep yellow, that remains consistent and untarnished even after long exposure to the elements. Unlike other metals that oxidize and change color when exposed to air and water, gold is a noble metal, meaning it resists corrosion. This resistance ensures its metallic luster, or shine, remains bright and reflective, even on the smallest flakes.
Gold is also notable for its extreme density, which is one of the highest among naturally occurring elements, with a specific gravity of around 19.3 for pure gold. This means gold is approximately 19 times heavier than an equal volume of water and significantly heavier than most other minerals found in river gravels, such as quartz, which has a specific gravity closer to 2.6. This weight is often the first characteristic noticed, as a small piece of gold will feel surprisingly heavy in the hand or sink rapidly in a gold pan.
Another defining property is gold’s remarkable softness and malleability, ranking between 2.5 and 3 on the Mohs hardness scale. This softness means a piece of gold will not shatter or crumble when pressure is applied, but instead will bend, flatten, or dent. Placer gold, having been tumbled and pounded by water and rocks for millennia, often shows evidence of this malleability through its flattened, rounded edges and irregular shapes. Real gold will deform under the point of a pin or knife, while most other minerals will break.
Common Forms and Sizes
The appearance of placer gold is directly influenced by the distance it has traveled from its original hard-rock source, resulting in several distinct morphological categories. The smallest particles are known as flour gold or gold dust, which are extremely fine grains, sometimes less than 0.1 millimeters in size. These tiny particles often appear suspended in water for a moment before slowly settling due to their small mass, despite their high density.
Slightly larger pieces are typically classified as flakes or fine gold, which are small, flat, and irregular fragments hammered thin by the mechanical action of the water. The characteristic flatness of these pieces is a result of the gold’s malleability, causing it to deform rather than break during transport. This shape increases the surface area relative to the mass, though they will still settle faster than non-metallic material of the same size.
The largest and most sought-after forms are pickers and nuggets. A picker is a small piece that can be picked up, while a nugget is a larger, naturally occurring chunk. These larger pieces are typically rounded and smoothed from rolling along the streambed, showing the effects of erosion and water-tumbling over time. Unlike crystalline minerals, placer gold rarely retains any sharp, angular, or cubic structure.
Distinguishing It From Look-Alikes
The primary challenge in identifying placer gold is distinguishing it from two common minerals that share a similar metallic color: Pyrite and Mica. Pyrite, often called “Fool’s Gold,” is an iron sulfide mineral that has a brassy or pale yellow color, which is distinctly less rich and warm than the deep yellow of real gold. Unlike gold, Pyrite frequently forms well-defined crystal shapes, such as cubes or octahedrons, which is a key visual difference from the irregular, water-worn shapes of placer gold.
The decisive test for Pyrite is its hardness and brittleness, as it ranks much higher on the Mohs scale, between 6 and 6.5. While gold is soft and deforms, Pyrite is brittle and will shatter, crumble, or break when scraped with a knife or pin. A further confirmation is the streak test: rubbing the mineral on unglazed porcelain will cause real gold to leave a metallic yellow streak, whereas Pyrite leaves a dark greenish-black streak.
Mica, particularly the golden-hued biotite or muscovite varieties, is the other common mimic. Mica is easily identifiable by its plate-like, flaky structure and extremely low density. When swirled in a pan of water, mica flakes will wash away easily or even appear to float due to their light weight and large surface area, contrasting sharply with gold’s tendency to immediately sink. A simple pressure test reveals that mica flakes are incredibly thin and separate into layers or smear into a paste when rubbed between the fingers, which gold will never do.