Larimar

Larimar is the tradename for a rare blue variety of the silicate mineral pectolite found only in Dominican Republic, around the city of Barahona. Its coloration varies from bluish white, light-blue, light-green, green-blue, turquoise blue, turquoise green, turquoise blue-green, deep green, dark green, to deep blue, dark blue and purple, violet and indigo and the larimar can come in many varieties and color mixes.

Larimar (Blue Pectolite)

General

Category Inosilicate mineral

Formula NaCa2Si3O8(OH)

Crystal system Triclinic

Crystal class Pinacoidal (1)

(same H-M symbol)

Space group P1

Unit cell a = 7.99 Å, b = 7.03 Å,

c = 7.03 Å; α = 90.51°,

β = 95.21°, γ = 102.53°; Z = 2

Identification

Color Shades of blue, blue-green

Crystal habit Tabular to acicular, radiating fibrous, spheroidal, or columnar; massive

Twinning Twin axis with composition plane, 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

Optical properties Biaxial (+)

Refractive index nα = 1.594 - 1.610 nβ = 1.603 - 1.614 nγ = 1.631 - 1.642

Birefringence δ = 0.037

2V angle Measured: 50° to 63°, Calculated: 42° to 60°

Dispersion r > v weak to very strong

History

In 1916, according to historical data collected by Dominican mining authorities, Father Miguel Domingo Fuertes Loren, who was then parish priest ofBarahona, was the first to discover blue rock. On November 29 of the same year, he requested a permit to explore and exploit the mine, but this was rejected since this type ofpectolitewas not known in the country. 

In 1974 on a beach on the coast ofBarahona, Miguel Méndez and Norman Rilling, aPeace Corpsvolunteer, rediscovered larimar. The locals who thought that this rock came from the sea, called it Blue Rock. The few rocks they found were remains that had been dragged to the sea by theBahoruco River. After a search, the origin of the rocks was found, which became the Los Chupaderos mine. This place is the same one that the priest had found in 1916. 

It was declared the national gemstone of theDominican Republicin 2011 by Law No. 296 of November 4 of that year. This gem is a symbol of the nation's identity and cultural heritage. The law designates that the Ministries of Energy and Mines, Environment and Natural Resources, Culture, and Tourism will allocate part of their budget to carry out activities that promote larimar nationally and internationally as a semiprecious stone that identifies the country.

In 2018, the National Congress declared November 22 of each year as “National Larimar Day” through Law No. 17 of April 23, 2018.

Physicochemical characteristics

Larimar has been classified as a fine stone since 1979. Its quality is assessed according to its color: the deeper the blue of the stone, the more sought-after it is.

Greenish colorations are also known but are not well regarded unless the green is intense. The crystallization of this pectolite occurred inside volcanic vents where the incandescent material was pushed by the gas. The exploitation of larimar therefore depends on the location of these vents. It is also found associated with other colors and other minerals. Red colorations in larimar indicate traces of iron. This variety is photosensitive, which is why larimar loses its blue coloration over time.

Geology

Larimar is a type of pectolite or a rock composed largely of pectolite, an acid silicate hydrate of calcium and sodium. Pectolite is found in many locations, but larimar has a unique volcanic blue coloration, which is the result of copper substitution for calcium.

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. 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 km (6.2 mi) southwest of the city of Barahona in the southwestern region of 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.

Jewelry

Larimar jewelry is offered to the public in Dominican Republic, and elsewhere in the Caribbean as a local specialty. Most jewelry produced is set in silver, but sometimes high-grade larimar is also set in gold.

Quality grading is according to coloration and the typical mineral crystal configuration in the stone. Larimar also comes in green and can have red spots, brown strikes, etc., due to the presence of other minerals or oxidation. The more intense the blue color and the contrast in the stone, the higher and rarer is the quality. The blue color is photosensitive and fades with time if exposed to too much light and heat.

Quality depends on the color. White is low quality, volcanic blue is high quality. High-quality jewelry uses gems that give their color between sky blue and volcanic blue. The greenish color is not well received, so it doesn't sell well, unless it's a very intense green. Some larimar rocks have traces of red, indicating the presence of iron.

Dominican jewelry designers such as Mónica Varela and Joarla Caridad have contributed to the popularization of larimar internationally.

Sourced from Wikipedia