This is how a typical day as a gemologist is like for me: I get a ton of messages with photos of rocks and crystals asking me if what they have are diamonds or rubies, sapphires, and emeralds. Sad to say, I’m always the bearer of bad news and tell them no. Aside from the fact the rough crystal formation is wrong (I’ll be discussing crystal formation in the near future, don’t worry!), Philippines is “too young” to be a source of diamonds and other precious gemstones and here’s why…
To start off the discussion, I’ll need to tell you about how diamonds form deep underground and how they’re “delivered” to the surface. It’s no secret that diamonds are made up of carbon. Yep, that’s the same chemical you can find in your pencil! The combination of high pressure and high temperature caused the diamond atoms to align or link together in a special way that made them virtually indestructible.
Where the Diamonds Form
Scientists believe that the earth is approximately 4.5 billion years old. To date, the oldest rocks that have been dated are 3.6 billion years old located in the Northwest Territories in Canada! Whilst diamonds themselves cannot be dated, scientists are able to determine the age of diamonds based on their inclusions.
As the diamond crystal was forming deep underground, about 140 to 190 kilometers beneath the earth’s surface (upper mantle), these carbon atoms were exposed to a temperature that ranged between 900℃ to 1300℃ and a pressure of 45 to 60 kilobars. A kilobar is a unit of measure that scientists use to measure extremely high temperatures. To put this to a context, at sea level, we are experiencing 1 bar of pressure so at 45 kilobars, that’s 45,000 times the pressure!
These conditions exist under large, geologically stable parts of the earth’s crust called cratons. Cratons are the oldest sections of the landmasses.
So three major ingredients need to exist for a diamond to form:
- Precise temperature
- Precise pressure, both IN THE RIGHT COMBINATION and
- Carbon rich environment
Diamond’s Source Rocks
Scientists discovered that diamonds form two different types of igneous rocks, a category of rocks formed from a molten state.
This igneous rock is where most diamonds form and probably existed from the time the earth first formed. The carbon in peridotites got released as these rocks melted due to the heat deep underground.
These are igneous rocks that are closer to the earth’s surface and are “younger” than peridotite. The carbon from eclogites probably came from ancient plants and animals. The eclogites got “dragged” deep underground due to earthquakes or shifts in tectonic plates, known as a process called subduction.
We now have the source of where diamonds come from. Now we need to learn how these diamonds are delivered to the surface where they can be mined!
There are two types of diamond deposits: Kimberlite and Lamporite. These igneous rocks were pushed up into the earth’s surface billions of years ago in a process called emplacement.
Kimberlite deposits tend to occur in the middle of cratons and are hence plentiful whilst lamporite deposits are found in the edges of cratons hence tend to be rarer. The Argyle mine in Australia, a known source of pink diamonds, is a lamporite deposit!
So now you know how diamonds are formed and what diamond deposits are.
Why are there no diamond mines in the Philippines?
The Philippine archipelago was formed 50 million years ago from various volcanic eruptions. And looking at our geography, we are nowhere near a “geologically stable” landmass; we’re surrounded by water! What we are is a country rich in minerals like gold, silver, copper, and nickel, to name a few. We also have an abundance of sedimentary minerals like feldspars, quartz, marble, and shale.