This thread and all the subsequent "Digging For Flavor" ones are just containers of quotes appearing in the Zendikar block (including Worldwake and Rise Of The Eldrazi).
Thanks to the advanced search engine of
magiccards.info which is so technologically advanced as to be undistinguishable from... Magic... I can look up a word in all the flavor text of all the cards of the series, excluding other sets.
The theme/word for this second search is "hedron": hedrons are gigantic stone-works, engraved with eldritch ruins, and often displaying some sort of glowing light from fissures.
And of course, they have a very geometric bi-pyramidal shape, octahedral actually. Hence the name "Hedron".

They are often "naturally" levitating, other times they are stuck inside cliffs (As you can see in the second image
here, where there's also some kind of force-field surrounding it) or they are hidden within bogs and swamps. They can be anywhere, and their purpose is mostly unknown to the the inhabitants of Zendikar, scholars included. A true mystery...

So here it goes:
QUOTES"We prepare for the known with daggers, rations, rope, and pitons. But we also prepare for the unknown with billycat tails, pikku roots, hedron chips . . ."
(Armament Master)
The ground erupted in time with the hedron's thrum, a dirge of the last days.
(Awakening Zone)
Only the Eldrazi mind thinks in the warped paths required to open the hedrons and tap the power within.
(Dreamstone Hedron)
The Roil redraws the world as it passes, leaving only the hedrons unchanged.
(Harrow)
Hedrons perplex minds both great and small.
(Hedron Crab)
The hedrons awoke along with the Eldrazi, forming superstructures that radiated overwhelming magic.
(Hedron Matrix)
"I don't care when the hedrons awoke. Why is the question that really matters."—Anowon, the Ruin Sage
(Hedron Scrabbler)
As the hedrons began to coalesce into colossal Eldrazi superstructures, the griffins were forced to seek new territory lest their aeries be crushed between the massive stone monoliths.
(Makindi Griffin)
"The structure gets bigger every hour, with hedrons coalescing even deep under the surface. If I could only get inside . . . ."
(Merfolk Observer)
"The scholars wept when we destroyed the hedron. I had no such pity. What would this world be like had we done so sooner?"—The War Diaries
(Naturalize)
"The sky hedrons are covered with tern nests. It's as though the birds have given up on the land altogether."—Ilori, merfolk falconer
(Welking Tern)
Explorers may find ways into the Sky Ruin, but they find its secrets well protected by shifting hedrons and Roil winds.
(Nimbus Wings)

UPDATE:
The article "The Tale of Tuktuk" had some info about the Hedrons concealed in it. I had dismissed it as info on the Goblin tribe of the same name and their strange golem-reborn leader, but it actually says something important about the Hedrons, specifying that even if they surely started as "the bars of the prison" of the Eldrazi, the vast minds of the three titans had managed to "surface", in the millennia that followed their imprisonment. And they aimed at the Hedrons more than anything, changing some of them (especially the ones underground from what I understood) to the point that Eldrazi magic was now clearly pulsating inside the stone artifacts. This is interesting because it makes the Hedrons something that can be either good or bad, something even more unpredictable than we first thought.

WHAT WE LEARNED
- The Hedrons are connected with the aberrant Eldrazi (beings that may be interpreted as god-like Far Realm entities, in D&D terms) which have been trapped inside Zendikar millenia before the present of the considered time-line.
- It is not clear if the Hedrons are wards against the Eldrazi, or if they were made by the Eldrazi themselves, or if they started as a ward and ended as a tool usable only by them, thus being dangerous, as the last quote (Naturalize) seems to imply.
- As suggested by their geometrical and perfect shape, Hedrons are an element of nearly unnatural order, in a world of nearly unnatural chaos. They tend to stay still when everything else changes and transforms thanks to The Roil (as clearly stated in Harrow).
When the Eldrazi awake though, the Hedron awake too and tend to "coalesce" into bigger structures, often combining into star-shaped forms made of 6 or more, or aligning in roder to constitute borders of some kind (as seen in artwork made for the lands of Rise of The Eldrazi, which is stunning by the way!)
- Hedrons are not only part of the landscape, but part of the ecosystem as well, as suggested by the illustartion of the Hedron Crab I put above!
Also, take a look at the last illustration below, for another way in that Hedrons are part of the ecosystem of Zendikar...
- Hedrons are surely nexuses of arcane or psychic power. They are also connected to dreams maybe (Dreamstone Hedron) or the reference to Dream as a force may be a hint at the fact that Hedrons are made to be usable only by creatures with completely different senses (also implied in the quote of Dreamstone Hedron). Chips of Hedrons are also probably used as consumable sources of power, as implied in the first quote (Armament Master).
- The fact that the Eldrazi are connected with the Hedrons should not be wise-spread knowledge, since the Eldrazi are meant to be Epic threats that appear in a world that had all but forgotten them, and even in the case the very "eldrazi" word is known by someone (before their physical return), it is surely misunderstood as something different from what they truly are.
- All in all, Hedrons are a plot-device, akin to Eberron's Dragonshards and the Draconic Prophecy. It is up to the Dungeon Master to use them and explain them as he/she considers a useful way in his/her campaign in Zendikar.
- Update: From the Tale of Tuktuk we learn that Eldrazi magic has influenced some of the Hedrons, even if they were originally constructed to be "the bars of their prison". So Hedrons are not only a plot-device, but a two-way plot-device, that can unpredictably be "aligned" with either the Eldrazi or the forces against them. Plus, we got to know that "hurting" the Hedrons can result in the springing of "Runeflare Traps".

ADDENDUM:
Hedrons also come in
cubical shape! Well, they're not true Hedrons anymore once they're cubical, I guess. They must be a sub-type of Hedrons
, and they appear both in Worldwake (in
Eldrazi Monument, that I put here below) and in Rise of The Eldrazi, making for what appear to be the most common "hedrons" of the swamps.
Enjoy this incredible piece of artwork!