Igneous Xenolith in Diorite ID'd

This video features the igneous structure called a xenolith--and this xenolith is located within the rock type called diorite. This video uses photogrammetry. A xenolith typically has a darker color than other parts of an igneous rock (because that locality contains more iron). A xenolith originates from rocks (known as "country rock") located along the wall of the magma conduit. This rock type, typically located deep below a volcano, became dislodged and thereafter part of the rising magma. Thereafter, the magma pushes the xenolith closer to Earth's surface--where the magma then slowly cools--along with the xenolith within.
Xenoliths can have either a rounded shape or an angular shape. This sample has a rounded shape (sort of like a potato). Xenoliths tend to have pointed, angular shapes upon breaking off from the magma conduit. However, the heat of the magma, will progressively start to melt the pointed areas of the angular-shaped xenolith. The angular areas of the original xenolith then becomes more subdued and rounded--with distance travelled from where it originated.
Additionally, areas where xenoliths originate, tend to have a higher iron content (and potentially a different mineralogy), than the magma surrounding the xenolith (which is closer to Earth's surface). Because xenoliths originate deeper within Earth's crust, xenoliths are often darker than the magma that contains it. Compositionally, xenoliths differ from the surrounding magma.
Architectural notes: This architectural stone was sold in the Seattle, Washington area. However, it is not from the Index quarry or other quarry in Washington State. I suspect it is from a quarry at Fox Island, in British Columbia, Canada (but I am not certain). This stone was cut into dimensional slabs, about 2.5 cm thick (or about 1 inch). Note there are some small red marker lines on this stone. These marker lines are meant as a guide to trim this stone slab into more rectangular dimensions. However, because this stone contains an architecturally unsightly xenolith, it was rejected as low aesthetic quality (despite being as structurally competent as similar dioritic stones).
Building stone designers prefer relatively even coloring/textures throughout the stone. But this dark xenolith disrupts the aesthetics of the general black- and- white mineral grains (throughout the other parts of the stone). Additionally, the different composition and mineralogy of the xenolith, compared to other parts of the stone, often will cause that locality to weather differently. Also, it may cause more difficulty in shaping the stone (if the stone chosen for stone carving). Stone carvers often called xenoliths "knots". This is comparative regard to the local structural and differences--such as in trying to carve wood that contains areas of tree knots.
Surrounding the xenolith is diorite. Diorite is a coarse-grain, intrusive, intermediate rock that is black and white in color. Diorite is an intrusive volcanic rock (igneous rock) that forms by cooling very slowly deep underground (often in a magma chamber below a volcano). This long cooling time allows the minerals in the rock to grow to a visible, coarse grain size.
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Identification information for the diorite part of this rock:
1) color: diorite is black and white. Note that by color alone, some types of diorites are confused with some types of granite--some which also have a black and white color.
2) grain size: coarse grain size
3) hardness: generally about as hard glass (for unweathered, clean samples). Note that hardness tests usually are oriented to pure minerals--and not to rocks. It will depend what part of the rock is chosen to try to scratch the glass.
4) composition: diorite is intermediate. So it contains a combination of plagioclase, hornblende, and biotite. These are black and white minerals, so that is why diorite is black and white color. Note again that diorite does not contain quartz, muscovite or orthoclase.
5) acid reactivity: does not react to acid
6) classification: it is an intrusive, intermediate igneous rock (volcanic)
7) density: it is about as dense as other igneous rocks
8) environmental association: typically is found in volcanic island arcs, or continental volcanic arcs (although diorite may be found in relatively young rift zones on continents too)
9) summary: if a rock has black and white mineral speckles, that interlock together--and does not react to acid contact--then it is probably either a granite or a diorite.
Music (CZcams Audio Library): Time to Spare (by An Jone)
Copyright by David Knoblach, 2023. All rights reserved (please contact me for permission to use).

[@GeologyDude]

Hello Rock People! This is Dave the Geology Dude! There is more to this video than just a spinning rock. There are detailed notes in the description area of this video. If you want more, longer length rock identification videos are on my CZcams homepage. Check them out, or leave a comment here!

[@mafic_taco7061]

Unsightly?! How dare they . They don’t deserve this gorgeous stone .

[@GeologyDude]

Some folks don’t like dark spots in their rocks. Ha ha. But I attended a field trip once, where geologists were going crazy looking at them.