Heddle's rock collection

Sphero basalt. This specimen is from an area on the Isle of Skye called Sgurr nam Boc, on the Minginish peninsula on the west coast of the island. Heddle travelled to Skye in search of zeolites and must have collected a small piece of host rock.

A garnet chlorite schist, greenish-silvery grey groundmass shot through with large, dark red garnets, with one face polished, from Hill of Maluth, Banffshire. This large specimen is on display in the Window on the World in National Museum of Scotland.

This large, heavy, polished specimen on display in the Restless Earth gallery in the National Museum of Scotland shows the contact between granite, an igneous rock, and gneiss, a metamorphic rock. It was collected in Balmoral in Aberdeenshire.

Saltire granite. This granite was collected by Heddle in the Persley Quarry near Aberdeen. It shows veins of quartz crossing in the form of a Saltire. See it on display in the Scotland: A Changing Nation gallery in the National Museum of Scotland.

Eruptive porphyry, from Davaar Island, Kintyre, Argyll. A porphyry is a volcanic rock which has a very fine groundmass surrounding much larger mineral crystals. These larger crystals would have formed first deep within the Earth whereas the rest of the material cooled quickly after the eruption locking in the old larger crystals.

Conglomerate, from Orkney. A conglomerate is a sedimentary rock that is made up of the rounded fragments of other rock types. The rock fragments became rounded and polished by tumbling around in a high energy water environment like a river or a beach. So in effect conglomerates are like hardened beach or river gravels.

Old Red Sandstone conglomerate, from Perthshire. Pebbles in this conglomerate are variable in size and not particularly well rounded. This may be due to the nature of the original rock type or because the conglomerate was deposited by a flood event that didn’t give the angular pebbles enough time to become polished.

Galena with slickensides, from Alston, Cumberland, England. Slickensides are smooth scours that form on a fault surface after one side has been dragged past the other side during an earthquake. They usually develop on rock faces but in this case they form an undulating surface across a single large mineral called Galena - a lead sulphide.

Small fault in hornblende gneiss, from Collafirth Voe, Shetland. A gneiss is a type of rock classed as metamorphic, which means it has been subject to pressures and/or temperatures that are higher than those found at the Earth surface or where it solidified (if it was originally an igneous rock). It shows the long and complex history that a rock can endure after it first forms on earth.

Contorted limestone, from Allt na Gonolan, Inverness-shire. Sometimes a rock can fracture if it is struck but if it is warmed and put under gradual pressure it can bend and contort. This limestone has been slowly contorted so the white vein which was originally nearly straight now curves around like a snake.

Pitchstone, from Corrie, Arran, Bute. This fine grained pitchstone has been forced ('intruded') into a Triassic sandstone. Close up the fine fibrous zeolite crystals can be seen forming radial patterns around other structures.

Syenite. A syenite rock can be described as a granite-like rock with silica either completely absent or present in very low quantities. Syenites are formed from igneous activity and are not common.