Shale is a hardened, compacted clay or silty clay that commonly breaks along bedding planes some of which are no thicker than paper. The best exposures are found beneath ledges of harder more resistant rocks such as limestone and sandstones. Most shales are soft enough to be cut with a knife and can be very brittle.

Crystalline rock, any rock composed entirely of crystallized minerals without glassy matter. Intrusive igneous rocks—those that congeal at depth—are virtually always crystalline, whereas extrusive igneous rocks, or volcanic rocks, may be partly to entirely glassy.

sedimentary rocks

Shales are often found with layers of sandstone or limestone. They typically form in environments where muds, silts, and other sediments were deposited by gentle transporting currents and became compacted, as, for example, the deep-ocean floor, basins of shallow seas, river floodplains, and playas.

Siltstone, hardened sedimentary rock that is composed primarily of angular silt-sized particles (0.0039 to 0.063 mm [0.00015 to 0.0025 inch] in diameter) and is not laminated or easily split into thin layers.

Diorite, medium- to coarse-grained intrusive igneous rock that commonly is composed of about two-thirds plagioclase feldspar and one-third dark-coloured minerals, such as hornblende or biotite.

sedimentary rock units

igneous rock

We thus have another link in the chain of evidence showing that gold is a constituent of granite and of plutonic rocks, and that such crystalline rocks may be the primal source of the gold, which is concentrated in veins. …

Granite is one of the hardest substances in the world. The only material that is harder than granite is a diamond. The hardness of granite makes it durable. Unlike other stone types, granite won’t crumble or break over time.

Granite is a light-colored plutonic rock found throughout the continental crust, most commonly in mountainous areas.

In rare circumstances, geologic conditions lead to an exceptionally pure limestone with no clay or sand mixed in. If a pure limestone undergoes metamorphism, a pure white marble is produced.

Granite is a light-colored igneous rock with grains large enough to be visible with the unaided eye. It forms from the slow crystallization of magma below Earth’s surface. This mineral composition usually gives granite a red, pink, gray, or white color with dark mineral grains visible throughout the rock.

Diamond

Granite is a strong stone because its mineral grains have grown tightly together during a very slow cooling period. Additionally, the quartz and feldspar that compose it are harder than steel. This makes granite desirable for buildings and ornamental purposes, such as gravestones and monuments.

talc

The hardest substance known is diamond. [but see note below] Diamond is made up entirely of the element carbon. (Another thing that is made entirely of carbon is graphite, one of the softest substances.) Diamond’s hardness is roughly 10.5-14.5 million psi.

Sedimentary rocks

Painite

emeralds

painite

Musgravite

Rubies are considerably rarer than diamonds but only in gem-quality form. The mineral that comprises rubies, sapphires, and emeralds is more common, but it’s the deep red shade a ruby comes in that is rarer. They’re much less common in jewelry than diamonds, which are always readily available.

The value and rarity of a gemstone directly relate to supply and demand. Both diamonds and opals are common, but that isn’t to say that all diamonds and opals are created equal. Because the value of most diamonds will be higher than opals, while high-quality opals are rarer than diamonds.

Top 15 Most Expensive Gemstones In The World

1. Blue Diamond – $3.93 million per carat. Blue diamond.
2. Jadeite – $3 million per carat. Jadeite.
3. Pink Diamond – $1.19 million per carat.
4. Red Diamond – $1,000,000 per carat.
5. Emerald – $305,000 per carat.
6. Taaffeite – $35,000 per carat.
7. Grandidierite – $20,000 per carat.
8. Serendibite – $18,000 per carat.