O Coro dos Minerais: poetic sonifications of minerals

O Coro dos Minerais (The Mineral Choir) is a residency project at the Museum of Mines and Metals in Belo Horizonte. As part of the Comciência program, I was selected with other artists to do a residency around the collection and the theme of the museum, using parts of their collection. Given the pandemic, some artists like me worked completely remotely and got help from the staff through Zoom sessions. With the Mineral Choir, I wanted to create sonification of minerals.

I decided to create sonifications of 10 minerals and consider them something like bird song: every mineral has its own unique song. I used a parametric mapping, meaning a datapoint of a mineral was mapped to a musical characteristic, for example, chemical elements were mapped to pitch, the length of the song was based on the age of the mineral et cetera. It is almost impossible for a person to listen to these sonifications and identify every chemical element of the mineral or other characteristics. However, it is possible to distinguish between the different songs in their entirety. So in this case, I consider this a case of a more poetic sonification than an exploratory sonification.

Because of the poetic aspect, I also linked it with Tetê, the resident extraterrestrial of the museum. I created a backstory that this creature has taught the staff how to listen to the minerals because humans could not hear them sing before. I also took cues from other stories like J.G Ballard’s Vermillion Sands, a novel about a paradisiac place for rich people where people grow singing plants. Another inspiration was The Mystery of the Third Planet, a 1981 Soviet movie about an interplanetary safari expedition to look for interesting animals for the Moscow zoo.

Tetê, the resident alien at the museum
Tetê, the resident alien

I will wrote a more detailed blog post about the technical process behind the work but you can check out the dedicated website. In the museum, people would scan a QR code and hear a random mineral playing. The choir aspect would come into being as people would put their phones next to each other with each one playing a different song. Each mineral is also linked to its Mindat.org page so people can learn more about each mineral.

For each mineral, I create a backstory based on their characteristics. For example, the Malachite has an enchanting song, making people look at it. Because of its green color, Tetê the extraterrestrial really likes it. Or the Crysoberyl: a true star. It repeats its chemical formula 8 times to make sure you remember it. 

Mappings and arranging

Using the mindat.org website and wikipedia for data, and with help of the museum staff, I chose 10 minerals, all discovered in Brazil and selected a group of data. I chose the hardness data as the initial data category: I roughly chose 10 minerals ranging from 0 to 10 hardness. Because I also wanted to chose subjectively on appearance, the final list had minerals that were within a hardness range, rather than an exact hardness. 

I initially wanted to map the hardness data to the pitch range of the song, so a mineral with a low hardness would only use the lower range of pitches and one with a higher hardness would have more octaves to choose from. but I realized that that would severely limit my compositional choices. Hence, I mapped the hardness data

I settled for the following mapping choices:

  • chemical composition: in the selected minerals, there were 25 different chemical elements (including impurities). I reduced that to 24 pitches in a quarter tone scale. So you have 24 notes per octave. I mapped two elements to the same note so I could fit in the 25 elements in 24 pitches. With this, I created the pitch sequence. I tried to hold on to the chemical formula as it is written out but in some cases, I changed the order in what it should be if the elements were laid out in space. For example, in 
  • Impurities: because they are also chemical elements, they are also mapped to pitch.
  • Class: each mineral is part of a class. This is mapped to the instrument. So you have minerals that have completely different melodies but are played by the same instrument so they sound somewhat alike. However, impurities are mapped to the same instrument for all minerals so you have some similarities. 
  • Age: the approximate age (we can never know the exact age of ancient object like these) constitutes the overall length of the song. The age is divided by 4000 and that gives us a number in seconds. The longest song are those of the Metazeunerite and Malachite (2.4 billion years old —> 600 seconds long), and the shortest is the quartz (108 million years old —> 27 seconds long). 
  • Z value: this is the number of times a chemical formula has to repeat to create the mineral structure in space. I used this to divide the song in equal parts that repeat. The Metazeunerite for example has a Z value of 2, so the song is divided in two parts. All notes have the same length by dividing the basic formula length by the number of elements in the formula. Example: The Spessartine’s song has a total length of 132 seconds. It has 11 symmetries, so the song is divided in 12 frases (as I call this) of each 11 seconds. As it has a Z value of 8, dividing the ‘frase’ in 2 parts of 62.5 seconds. 62.5 divided by the number of elements (
  • Crystalographic structure:  The number of mirror symmetries decide the further division of each repeating part in smaller sections.  The first mirror is usually the sequence played backwards and in subsequent ones, I tried to mirror notes as well around a central axis although I had to take some liberties here. In case there were more than two symmetries, I transposed notes with octaves. 
  • Tenacity: when you hit a mineral the reaction is called the tenacity. A mineral can for example be brittle, so it breaks into very small pieces. Or elastic: it bends but returns to its original shape, or flexible: it bends but stays in the new shape. In my selection, I had three types of tenacity: elastic, flexible, brittle. I mapped this to the stereo image: brittle resulted in chaotic panning, elastic changed panning gradually, and flexible only changed its panning parameters at the mirror phase (resulting from the crystallographic structure).
  • Lustre: the appearance of the mineral decided some extra parameters and effects. For example: for the submetallic lustre in Grafite, I used effects that would create a metallic resonance. For earthy lustre, I used a noise generator and a vinyl noise effect.
The Spessartine, one of my favourite minerals. It looks a bit like The Thinker by Rodin
The Spessartine, I like the resemblance to Rodin’s the Thinker

While I tried to stay truthful to the parameters, it is very well possible that I changed a few things because it sounded better or that I did not perfectly map the data. This is acceptable for name as it is poetic freedom. In the end, these sonifications are not meant for listeners to grasp every characteristic separately, but rather the whole. Each song is unique, yet share similarities with others. 

To arrange the songs, I used Ableton Live, where I put the pitches in 2 tracks , with the second one transposed a quarter tone higher to allow for the division of the octave in 24 pitches.  Instrumentally, I used mainly the Native Instruments Absynth and Massive VSTs, and for the effects I used Reaktor and Ableton’s standard effects. 

Visit the exhibition

You can visit the whole exhibition via https://2021.programacomciencia.org.br or if you want to go directly to the mineral choir, you can go to ocorodosminerais.com. The website itself is only available in Portuguese. I also made the sonifications available via Soundcloud in the following playlist.


I would like to thank the museum for the opportunity and the museum staff, mentors, and curators for their help and advice into making this project come alive.

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