Monday, 16 February, 2026/Edition 98

Today is Presidents’ Day in the United States, so this week’s edition starts off with an homage to the Naturalist President, Theodore Roosevelt.

We will also review some recent studies of Mountain Pass carbonatite rocks. These rocks supplied the bulk of rare-earth elements (REEs) globally from 1965–1985. Mountain Pass Mine in California is still the largest known igneous body of REEs in the world.

But before we dig in, good news for rock scientists: South Africa’s Council for Geoscience has launched Africa’s first Virtual Core Library.

Rasoul Sorkhabi

Editor, Core Elements

Naturalist President Remembered

Theodore Roosevelt National Park and book cover of The Naturalist. Wikimedia Commons.

Theodore Roosevelt was born in 1858 in Manhattan and died in 1919. He served as the 26th U.S. President from 1901 to 1909.

Darrin Lunde’s fascinating biography, The Naturalist: Theodore Roosevelt details the life of Roosevelt as a naturalist and explorer. Here are some highlights:

Young naturalist: At age 9, Roosevelt opened his home-based Roosevelt Museum of Natural History and wrote a paper on insects.

Graduation, marriage, and political life:

• In 1876, Roosevelt entered Harvard University and graduated in 1880.

• The same year, he married Alice Lee and joined the Republican Party—the party of Abraham Lincoln, whom Roosevelt’s father admired.

North Dakota connection: After Roosevelt lost both his mother and first wife on 12 February 1884, he left New York, bought a ranch in the Badlands of North Dakota, and led a cowboy life for two years.

• Theodore Roosevelt National Park (formerly the Roosevelt Recreation Demonstration Area in 1935) is located in the badlands of western North Dakota.  

• Library: On July 4, 2026, on the 250th anniversary of the founding of the United States, the Theodore Roosevelt Presidential Library will open in Medora, North Dakota.

Trustbuster: While president, Roosevelt implemented the 1890 Sherman Antitrust Act against trusts, which monopolized the railroad, meat, and oil industries.

Nobel Prize: In 1906, Roosevelt won the Nobel Peace Prize for his efforts to end the Russo-Japanese War. Roosevelt was the first American to win a Nobel Prize.

Conservation: During this presidency, Roosevelt protected about 230 million acres of public land by establishing:

• 150 national forests

• 51 federal bird reserves

• Four national game preserves

• Five national parks

• 18 national monuments

Prolific author: Roosevelt was well-read and published more than 40 books in his lifetime. His letters were published in eight volumes by Harvard University Press.

Into the Amazon: From 1913–1914, Roosevelt, with his son Kermit and Brazilian Colonel Cândido Rondon, led an expedition to survey the Rio da Dúvida (River of Doubt) in the Amazon Basin.

Mount Rushmore:

• Roosevelt’s face—alongside those of George Washington, Thomas Jefferson, and Lincoln—was sculpted into the Black Hills in South Dakota.

• Mount Rushmore is a 1.6-billion-year-old granite uplifted during the Laramide orogeny.

Go deeper: Watch the History Channel’s documentary film and read David Brown’s new biography on Roosevelt.

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Carbonatite Rocks of Mountain Pass Mine in California

Mountain Pass Mine in California and carbonatite rock/Wikimedia Commons

Carbonatite is an igneous rock, but it contains more than 50 percent carbonate minerals.

Fast facts:

• Carbonatites are rare.

• They host the largest REEs in any rock type.

• Their genesis is shrouded in various hypotheses.

Mountain Pass (MP) in the Mojave Desert of California has excellent exposure of carbonatites.

• The Mojave province spans southeast California and extends into Nevada, Utah, and Arizona.

• The province is a complex assemblage of 1.8- to 1.6-billion-year-old metamorphic rocks intruded by REE-rich igneous stocks and dikes and emplaced at 1.4 billion years ago.

Two recent papers shed light on this fascinating rock and mine. Let’s take a look.

Study #1. Geochemical Signatures of Mantle Source

Erin Benson and colleagues in Lithos have described the geochemical signatures of MP rocks and discussed their origin.

What they did: The researchers collected 31 carbonatite and 26 alkaline silicate samples from MP and analyzed them for whole-rock major and trace elements, Rb-Sr and Sm-Nd isotopes, and in-situ zircon Lu-Hf isotopes.

What they found:

• Alkaline silicate and carbonatite rocks are enriched in large ion lithophile (incompatible) elements (such as potassium, rubidium, cesium, barium, strontium, thorium, and uranium) and light REEs.

• The mantle source was enriched in incompatible elements by metasomatism (rock alteration by hydrothermal fluids).

• Alkaline silicate and carbonatite melts were generated through partial melting from a shared mantle source region.

• Partial melting of deeply subducted carbonated sediments was followed by post-collisional melting and substantial crustal contamination.

• Tectonic consideration suggests that there was a time interval of about 300 million years between subduction and post-collisional carbonatite emplacement.

Why it matters: This study supports the idea that carbonatites are derived directly from the mantle by partial melting of carbonated peridotite.

It also refutes two other mechanisms proposed for the genesis of carbonatites:

1. Derivation from alkaline silicate melts through liquid immiscibility

2. Precipitation of carbothermal residue following fractional crystallization of carbon dioxide-enriched alkaline silicate melts

Study #2. Heterogeneous Mineralogy of Carbonatites

Kathryn Watts and Allen Anderson of the U.S. Geological Survey report on details of REE-rich ore minerals in MP carbonatite in American Mineralogist. 

What they did:

• The researchers collected carbonatite samples from igneous stock and dikes near the MP mine.

• They analyzed them for whole-rock major and trace elements.

• They also examined mineral-scale textural and chemical data obtained from scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and micro-Raman spectroscopy.

What they found:

• Bastäsite, a fluorcarbonate [REE(CO₃)F] mineral, is a predominant host for light REEs.

• Other minerals that host REEs include:

  • Hydroxylbastnäsite [REE(CO₃)OH]

  • Parasite [Ca(REE)₂(CO3)₃F₂]

  • Synchysite [Ca(REE)(CO₃)₂F]

  • Röntgenite [Ca₂(Ce,La)₃(CO₃)₅F₃]

  • Sahamalite [(Mg,Fe)(REE)₂(CO₃)₄]

• Hydrothermal processes of REE mineralization in the igneous stock are evident by cross-cutting vein textures, brecciation, and hydroxylation of bastnäsite.

• Late-stage fluids particularly impacted carbonatite dikes.

Why it matters: This study documents a complex spectrum of REE-bearing carbonate minerals and intermediate mixed-layer structures in MP, which must be considered in mineral exploration.

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