Exploring the granite of Halk Hakydasy

Ashgabat is famous for its monumental architecture and extensive use of pale ornamental stone. At the Halk Hakydasy Memorial Complex, however, the visitor encounters a strikingly different colour.

The walls of the Watan Mukaddesligi Museum are covered with polished pink to reddish granite. The enormous surface provides an excellent opportunity to look beyond the colour and examine the individual minerals that make up this rock.

The Halk Hakydasy (“People's Memory”) Memorial Complex was opened in 2014. It commemorates those who died in the Battle of Gökdepe, the Second World War and the devastating Ashgabat earthquake of 1948. 

For this EarthCache, we will concentrate not on the history represented by the monuments, but on a much older history recorded in the rock covering the museum.

What is granite?

Granite is an igneous rock. It forms when silica-rich molten rock cools and crystallises below the Earth's surface.

Unlike volcanic rocks, which may cool very quickly after reaching the surface, granite normally cools slowly underground. This gives its minerals enough time to grow into crystals large enough to be seen with the naked eye.

A typical granite contains three important groups of minerals:

Feldspar – commonly white, cream, grey or pink. Potassium-rich feldspar is often responsible for the pink or reddish appearance of granite.

Quartz – commonly grey, colourless or slightly translucent. Quartz often has a somewhat glassy appearance.

Dark minerals – commonly biotite mica and/or amphibole. These produce the black or very dark grains scattered through many granites.

The exact proportions of these minerals vary from one granite to another.

Why is this granite red?

The striking colour of a red granite is generally associated with its feldspar.

Potassium feldspar can naturally appear pink or reddish. Tiny amounts of iron within or associated with feldspar can intensify this colour. Iron in an oxidised state can produce reddish tones, somewhat analogous to the way iron oxides colour many rocks and soils red.

Consequently, a granite does not need to consist of a red mineral throughout. A large proportion of pink-red feldspar crystals can visually dominate the entire rock.

Look closely at the granite here and the apparently uniform red wall begins to look very different: it becomes a mosaic of individual crystals.

Crystals tell us how the rock formed

Crystal size provides an important clue to the cooling history of an igneous rock.

When magma cools slowly underground, crystals have considerable time to grow. The resulting rock therefore has a coarse-grained texture in which individual mineral grains can usually be distinguished with the naked eye.

When molten rock cools rapidly at or near the surface, there is much less time for crystals to grow and the resulting rock is generally much finer grained.

Geologists use the term phaneritic texture for an igneous rock containing crystals large enough to be readily seen without magnification.

The granite at Halk Hakydasy therefore allows you to use its texture to reconstruct part of its geological history.

One rock – many crystals

From a distance the walls may appear almost uniformly pink or reddish. Close inspection tells another story.

Individual crystals have different colours, shapes, sizes and reflective properties because they represent different minerals. Even slabs cut from the same general type of ornamental stone do not necessarily look completely identical.

This variation is one of the differences between natural stone and an artificial building material.

Logging requirements

Please examine the polished pink-red granite slabs covering the exterior wall of the Watan Mukaddesligi Museum. Do not use the dark sculptured (people, horses, canons etc) relief panels for your observations.

Send your answers to me preferably through the Geocaching Message Center. You do not need to wait for permission before logging your find.

1 – A rock made of crystals

Look closely at the granite and identify the three main colours of mineral grains that you can see.

Which colour appears to occupy the greatest proportion of the rock?

Using the information in the listing, which of these grains do you think represents feldspar, quartz and the dark mineral(s)?

2 – The size of the crystals

Estimate the typical size of the visible crystals in millimetres. You do not need to measure individual crystals precisely.

Are most crystals approximately the same size, or is there considerable variation?

Based on their visible size, did this rock cool relatively quickly at or near the Earth's surface, or slowly underground? Explain your reasoning.

3 – Why is the granite red?

Which mineral visible in the rock appears to be mainly responsible for its overall pink-red colour?

Explain why this mineral can give granite a pink or reddish appearance.

4 – One wall, many slabs

Step back and compare several neighbouring granite slabs, then examine them more closely.

Are their colour, crystal size and proportion of dark minerals completely identical?

Describe at least one variation you can observe between different slabs.

5 – Photo

Please include a photograph showing that you visited the Halk Hakydasy Memorial Complex. The photograph may show yourself, your GPS, your geocaching name or another personal object.

Please avoid close-up photographs of the granite that reveal the answers to the observation tasks.