Larimar: Uncovering the Mystery of the 'Blue Rock'!

Larimar is actually a rock, being composed of more than one mineral, but is mostly composed of pectolite, an acid silicate hydrate of calcium and sodium. It has been given the trade name "Larimar".

Pectolite is found in many locations, but larimar has a unique volcanic blue coloration, which is the result of copper substitution for calcium.

Larimar found exclusively in the Caribbean, on the island of Hispaniola. It is only found in a dormant, volcanic mountain range in the Baoruco Mountain of the Dominican Republic.

Miocene volcanic rocks, andesites and basalts, erupted within the limestones of the south coast of the island. These rocks contained cavities or vugs which were later filled with a variety of minerals, including the blue pectolite. These pectolite cavity fillings are a secondary occurrence within the volcanic flows, dikes, and plugs. 
Larimar: Uncovering the Mystery of the 'Blue Rock'!
 Polished Larimar.
Photo: Lovingthyselfrocks/Instagram
When these rocks erode, the pectolite fillings are carried down the slope to end up in the alluvium and the beach gravels. The Bahoruco River carried the pectolite-bearing sediments to the sea. The tumbling action along the streambed provided the natural polishing to the blue larimar, which makes them stand out in contrast to the dark gravels of the streambed.

Los Chupaderos

The most important outcrop of blue pectolite is located at Los Chupaderos, in the section of Los Checheses, about 10 kilometers southwest of the city of Barahona, in the south-western region of the Dominican Republic. It is a single mountainside now perforated with approximately 2,000 vertical shafts, surrounded by rainforest vegetation and deposits of blue-colored mine tailings.

Larimar, also called "Stefilia's Stone", coloration varies from white, light-blue, green-blue to deep blue. The color of Larimar is caused by copper inclusions. Its color is rarely solid; it is almost always blue with interconnecting white lines and rough circles. A radiating pattern of crystal needles can often be observed within the Larimar. The blue color can vary in intensity from very light to greenish-blue to deep sky blue. Deeper blue colors and less white are more desirable.

Pectolite is also known in serpentinites and peridotites of ophiolitic complexes ; it is frequently associated with prehnite, datolite and different zeolites.

Pectolite is usually a soft and very delicate mineral composed of dense radiating fibers, but sometimes the fibers are tough and interlocking and make it very solid. The Larimar variety is of the tough type hence its ability to withstand carving and faceting.

Although Larimar has a very attractive color, it is a soft gemstone and is easily scratched. Its color may also fade upon prolonged exposure to strong sunlight. This, combined with its scarcity, limit its popularity as a mainstream gemstone.

Pectolite commonly occurs as acicular crystals (up to 15 cm), rarely completed and grouped into radiated bundles or fibroradiated urchins. Large prismatic crystals are much rarer.

Its luster is pearly to vitreous, it is mostly colorless to white, sometimes gray, greenish or yellowish, it is called larimar when it is blue and massive.

There is a legend that Larimar was originally discovered in 1916 and its locality subsequently forgotten. In 1974, Norman Rilling, a visiting member of the US Peace Corps, found the locality together with Miguel Méndez, a Dominican native. Together they named this stone "Larimar", which is a combination of "Larrisa" (Méndez's daughter's name) and "mar" (sea in Spanish). Due to its scarcity and limited source, Larimar is difficult to obtain outside of the Caribbean.

Finally, Larimar has been used in the same manner as turquoise and is even seen in contemporary Native American jewelry. It has been quite versatile in its applications to other jewelry varieties. Larimar offers a different color to those who like polished stone jewelry.
Larimar: The Blue Stones of Atlantis
Cut Larimar (var. pectolite) From The Dominican Republic
Larimar: The Blue Stones of Atlantis
Larimar. Credit: Daniel Virgadaula

Properties of Larimar:

Chemical Formula: NaCa₂Si₃O₈(OH)
Crystal System: Triclinic
Color: Shades of blue, blue-green
Crystal habit: Tabular to acicular, radiating fibrous, spheroidal, or columnar; massive
Twinning: Twin axis [010] with composition plane [100], common
Cleavage:Perfect on {100} and {001}
Fracture: Uneven
Tenacity: Brittle; tough when compact
Mohs scale hardness: 4.5 - 5
Luster: Silky, subvitreous
Diaphaneity: Translucent to opaque
Specific gravity: 2.84 - 2.90
Associated Minerals are various zeolites, prehnite, calcite, datolite and serpentine.
Other Characteristics: Splinters of pectolite do not bend and are brittle. They are also sharp and can easily puncture the skin if not handled properly. Also some specimens can be triboluminescent.
Notable Occurrences include Lake Co., California and Paterson and Franklin, New Jersey, USA; Bahamas, Dominican Republic; Italy and England.
Best Field Indicators are crystal habit, association with zeolites, brittleness and cleavage.

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