Formed well below the earth's surface hundreds of millions of years ago as molten rock from the mantle tried to force its way to the surface, the rock that is now Mount Buffalo formed a huge bubble underground and then cooled slowly, forming granite with its large crystal structure and unusual weathering characteristics

 

When this process occurs the overlying rocks tend to peel away like an onion, which accounts for the rounding of Mount Buffalo's cliffs and boulders. The most common minerals in this type of rock that are easy to see are quartz (white and hard), felspar (often cream, light pink or brown) and mica (the black or silver shiny parts).

Gold

In the 1850s early miners searched but found no gold on the mountain. Gold rarely forms in granite, and when it does it's mostly in intrusive dykes that occur later than the host rock formation. The heat and pressure of the molten granite forcing its way into the overlying sedimentary rocks is, however, believed to be one of the causes of the mineralization in the metamorphic geology surrounding the granite mass. The areas in the Buckland Valley just to the East of Mount Buffalo were rich gold-bearing areas.

Valuable minerals associated with granite

Tin ore (most commonly in its oxide cassiterite) is one of the common valuable minerals found in Granites, the Beechworth Granites (nearby) being a major producer of this metal for the state. Luckily - or mining may have damaged the mountain top - there were no valuable minerals found on the mountain. Other minerals of gems associated with granite type rocks (many can also be found at Beechworth) include Amethyst, Citrine and other Quartz crystals, Tourmaline, Topaz, Molybdenite (used to harden steel and as a dry lubricant) and a range of other interesting and sometimes radioactive minerals.

Radioactivity

Granite is mildly radioactive and has a range of uranium family minerals in tiny amounts spread throughout, not at dangerous levels however. The luminous hands on a wristwatch have higher radiation levels!

Erosion and time

Over time wind, water and ice have eroded away the overlying rock leaving behind the mountain's amazing granite formations. The sedimentary rocks that originally covered the area (and some of the metamorphic rocks of the contact zones) can still be seen at places on the road to the mountain top.

Pegmatites and dykes

Pegmatites and dykes can be found in the granites of Mount Buffalo by the observant person, although they are not as gem crystal rich as the pegmatites of the Beechworth Granites.

Xenoliths

Inclusions of the original overlying rock that became caught in the molten rock (called Xenoliths) are also interesting and quite common. These are the rounded edge darker and often micro-crystalline patches that can be seen on the surface in places. They are easy to see on The Horn walking track.

The colour of the rock

The browns and greys and other colours that are common when you look at Mount Buffalo's boulders and pinnacles are actually lichens and mosses. The true colour of the granite can be seen below some of the lookouts, where chemicals from the metal and concrete have killed the living plants leaving the natural rock colour, or where the rock has broken away recently.

Landslides and cliff collapse

Granite rock weathers much more slowly than many other types and also the rounded surfaces tend to provide stability, so rock falls and the like rarely occur. Weathering is a slow process in granite country. There is a good example of a large landslide (about the year 1999) along the road to Cresta Valley. Pass the Cathedral Car park and when continuing on look back at the southern slopes of the Castle feature and you will see a HUGE boulder half way down a massive scree slope. This boulder has little lichen discolourations as it ended upside down and now sits a different colour to its new fellows. Driving around the base of Mount Buffalo on the Buckland, Ovens or Buffalo River roads will also reward the observant with evidence of landslips and slides. Most of these are the result of increased erosion of the steep slopes after the recent bushfires.

Granite caves

Caves in granite are quite rare (limestone caves are more common) but Mount Buffalo has a number of them, notably the underground river cave and two other smaller caves (one vertical). By definition a cave must have areas of total darkness so the many cracks and crevices and overhangs are just that and are not true caves.