The Goldschmidt System

This system groups elements based on their chemical affinity, basically "who they like to hang out with" in a molten blob of planetary material. When the earth was still molten, these elements separated based on these affinities like water and oil, into different layers.

Chemical Logic

1. Lithophiles: Prefer to donate electrons (Ionic Bonding)
2. Chalcophiles: Prefer to share electrons (Covalent Bonding)
3. Siderophiles: Prefer to exist as neutral metals (Metallic Bonding)
4. Atmophiles: Prefer not to bond or form weak bonds (Van der Waals forces)

The Four Categories

Siderophile (Iron-Loving)

Heavy metals that dissolve easily in molten iron

• Bonding: Metallic
• Key Elements: Iron, Nickel, Cobalt, Gold, Platinum, Palladium, Iridium
• Location: Core
• Geochemical Consequence: Gold and Platinum are rare in the crust not because they are rare in the Universe, but because they all sank to the core when Earth differentiated.

Lithophile (Rock-Loving)

Elements that love Oxygen. They form light, stony silicates and oxides.

• Bonding: Ionic (Strong bonds with oxygen)
• Key Elements: Silicon, Aluminum, Magnesium, Calcium, Sodium, Potassium
• Location: Crust and Mantle
• Geochemical Consequence: The vast majority of the rock you see on hiking trails is composed of Lithophile elements.

Chalcophile (Copper-Loving / Sulfur-Loving)

Elements that bond well with Sulfur, Arsenic, Selenium

• Bonding: Covalent (Softer bonds)
• Key Elements: Copper, Zinc, Lead, Silver
• Location: Form distinct deposits of ore (sulfides) within the crust but do not dissolve well in silicate magmas or iron cores.
• Geochemical Consequence: Most of our industrial metals (batteries, wiring) come from mining sulfide minerals.

Atmophile (Gas-Loving)

Volatile elements that prefer to remain as gases or liquids on the surface.

• Bonding: Weak Van der Waals forces.
• Key Elements: Hydrogen, Nitrogen, Carbon, Nobel Gases
• Location: Atmosphere and Hydrosphere (Oceans)

"Iron" is tricky

Iron comes up at multiple places:

• it defines Siderophiles and forms the Core
• it is a major Lithophile (is in Pyroxene and Olivine in the Mantle)
• it forms Chalcophile minerals (Pyrite)

Iron is abundant so that it can act as a "buffer". Once the core is full of iron, the leftover iron oxidizes to become a lithophile component of the mantle.

Question and Answers

What are the four categories of the Goldschmidt Classification system?::Siderophile, Lithophile, Chalcophile, Atmophile.

What does "Siderophile" mean literally, and where are these elements concentrated in the Earth?:::Iron-loving; concentrated in the Core.

What does "Lithophile" mean literally, and where are these elements concentrated in the Earth?:::Rock-loving; concentrated in the Silicate Earth (Crust/Mantle).

What does "Chalcophile" mean, and with which element do these metals prefer to bond?:::Copper/Ore-loving; they prefer to bond with Sulfur.

What type of chemical bond characterizes Lithophile elements?::Ionic bonding (forming stable oxides/silicates).

What type of chemical bond characterizes Siderophile elements?::Metallic bonding.

Why are Precious Metals (Gold, Platinum, Iridium) rare in the Earth's Crust?
?
Because they are Siderophiles. During the Earth's formation, they partitioned strongly into the molten metallic iron and sank to form the Core.

Which element acts as a buffer, behaving as a Siderophile, Lithophile, AND Chalcophile depending on conditions?::Iron ($\text{Fe}$).

Classify the element: Silicon ($\text{Si}$).::Lithophile.

Classify the element: Gold ($\text{Au}$).::Siderophile.

Classify the element: Copper ($\text{Cu}$).::Chalcophile.

Classify the element: Argon ($\text{Ar}$).::Atmophile.