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Description
Aragonite and calcite with pocket of calcite rhombsLocale: Sidi Ayed, Fs Mekns Region, Morocco Approx dimensions: 3. 5 x 2 x 2" Approx size: 425g (0. 9 lb) Calcite and aragonite are polymorphs of one another, meaning that the same chemical composition (calcium carbonate) has crystallized into different crystal structures (trigonal and orthorhombic, respectively). Calcite and aragonite often grow together, and the two minerals are also frequent paramorphs of one anothera pseudomorph of the same
Locale: Sidi Ayed, Fès-Meknès Region, Morocco
Approx dimensions: 3.5 x 2 x 2"
Approx size: 425g (0.9 lb)
Calcite and aragonite are polymorphs of one another, meaning that the same chemical composition (calcium carbonate) has crystallized into different crystal structures (trigonal and orthorhombic, respectively). Calcite and aragonite often grow together, and the two minerals are also frequent paramorphs of one another—a pseudomorph of the same chemical composition and retaining the original crystal shape but with different crystal structure, created through a change of conditions such as heat or pressure. There is understandably some confusion distinguishing what is calcite, versus aragonite, or a paramorph, or some hodgepodge of all of the above.
Which is all to say, this specimen falls somewhere in that ‘hodgepodge’ category. The matrix is partially calcite, and rhombohedral patterns can be seen in places. It appears aragonite formed over calcite points on the top which then partially or wholly dissipated, leaving some of the aragonite points hollow. There is a small pocket on the back of the piece filled with small white calcite rhombs.
UV reactivity The aragonite will give a moderate reaction under 365 nm UV light, fluorescing a light taupe color. The calcite will stand out in comparison, fluorescing a strong peachy-red color.
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4.4 ★★★★★
Based on 2035 reviews
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Product Reviews
★★★★★ 1
Do Not Buy Denon Products
Style: AVR-X1800H
In search of a new A/V receiver, I sought recommendations from my friend, a professional custom home theater installer. He strongly suggested a Denon model, citing its exceptional quality and robust customer support. Regrettably, my experience with this receiver has been diametrically opposed. Upon connecting all components and completing the setup instructions, the unit commenced malfunctioning immediately. Subsequently, when all components were shutoff after I finished watching a program, the receiver turned itself back on. Occasionally, it would also turn on the TV too. Fortunately, I was present during these occurrences. I contacted Denon support, providing a comprehensive description of the issue, including the steps I had taken to resolve it, which entailed restoring the unit to its factory settings. Regrettably, the support representative was unable to provide any information regarding the underlying cause of the problem or offer a solution. When I informed him of my option to return the unit until January 31, 2026, his response was that this may be the most appropriate course of action. Upon looking at reviews of this receiver and Denon receivers in general, this has been an ongoing issue for some time. Therefore, I would not recommend purchasing Denon products.
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Reviewed in the United States on January 14, 2026
★★★★★ 5
An excellent product!
Style: AVR-X2800H, Style: AVR-X2800H
Happy and satisfied does not begin to describe my satisfaction in this Denon product! Setup was a snap, instructions were detailed, and the finale results were amazing. And yes I’m running a full 7.1 setup, sounds fantastic….
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Reviewed in the United States on May 19, 2026
★★★★★ 5
Easy Set Up and Great Sound Distribution
Style: AVR-X3800H
I replaced an old Onkyo 535 with this Denon. It was a significant upgrade. There is zero noise, the Bluetooth is easy to use and provides excellent sound, and the HDMI circuitry is outstanding. The eARC capability is compatible with 2.1 HDMI, and it works seamlessly. Of note, I really like the way it provides the best sound configuration automatically for each source, and I don't have to switch around to find the best sound option. For example, if the source is compatible with Atmos, it provides Atmos. If it's only compatible with Dolby surround, it switches to that. Finally, the distribution of sound is superb. I have a 7.1 speaker configuration of mostly mid-level speakers, and the Denon uses them to their fullest. Rear sounds come clearly from the rear...same with each side, etc. And most of all, I don't have to tweak the system to get that. I just used the provided microphone and ran the set up (which was really easy), and I have really great sound. This unit is a good value.
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Reviewed in the United States on January 28, 2026
★★★★★ 4
Expensive, but nice
Style: AVR-X4800H
I previously owned a Denon AVR-2808ci since 2008. That model's remote control didn't work well, and all controls were unnecessarily convoluted, so I was hesitant to buy another Denon. The thing that made me give them another chance is that the sound quality was nice, and I was hoping their engineers learned from their mistakes. I'm glad I gave them the chance.
This new model, the AVR-X4800H, also has excellent sound quality; however, unlike the old one I had, the controls on both the receiver itself, and especially on the remote control, are significantly improved. The controls are intuitive, and everything works perfectly.
That alone made me happy with the purchase; however, the ability to run 4k @ 120 hz for video gaming, and with extra HDMI ports they have here, all added to that value quite a bit. Then, in addition to that, the old model I had ran super hot. In fact, so hot, from just basic usage, it fried itself three different times in the span of a couple weeks (during the winter time), and it kept being repaired under warranty, until they replaced the top grate with one that allows more ventilation. However, this new model doesn't appear to suffer from that same issue. It gets pretty warm, but nowhere near what the old one did -- and I'm using the same Bose Surround Sound system with the new one.
That said, as a precaution, I went ahead and ordered an AC Infinity AirCom to put on top of it, to assist with cooling/ventilation, which has worked wonderfully as well. No the tempts on this Denon AVR have never gone above 87 deg, even on a warm room on the third floor during the late spring / summer time.
The other hesitancy I had was the price tag. I only purchased it because it was on a "25% discount", from $2500 down to around $1850. Granted, it was similar when I purchased the other one 15 years ago, but it's just an awful lot of money, in my humble opinion. I would say it was borderline on whether I would buy it for this amount, and if it went up at all, I wouldn't have purchased it. I may not purchase it again for this price, especially if I have one already that is working well -- it was only the wonky one that I already owned, that I just wanted to get rid of, that put more pressure to give them one more chance. With a working device, I probably wouldn't pay these prices again. But, if it were a few hundred dollars cheaper, then I probably would buy it again.
Hopefully this helps someone. It's a great device, just a bit expensive. And, if you get it, I would still recommend getting a top cooling fan for it.
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Reviewed in the United States on June 13, 2024
★★★★★ 5
Solid Next-Generation AVR.
Style: AVR-X2800H
I bought this for my 2.1 system used for TV (4K with 120 Hz), movies, video games (4K with 120 Hz), turntable, and digital audio. I have previously used Denon, Marantz, and NAD AVRs. I was using an old NAD without HDMI, and I really wanted everything to synch up.
I tried out a stereo receiver since I am only running a 2.1, but I didn't mesh for me. It was fine, but I felt it was lacking especially around multi-channel audio and the lack of an LFE output for the sub.
The 2800H was very intuitive and easy to set up right out of the box. Hooked up to a TV, it runs through everything step-by-step. After the initial setup, I downloaded and ran a firmware update. When I finally got to use my ears, the sound was already superior to what I had from the mid-2000s 60-watt-per-channel NAD AVR with an external Bluetooth/DAC and PCM cable from the TV AND the brand-new, 2023 model HDMI-equipped stereo receiver (that cost me more than the 2800H). After running Audyssey, the sound only got better. Then, I set up my 2 front speakers on a bi-amp setting, utilizing two of my unused channels to drive my woofer and tweeter with discrete power sources.
The eARC and settings makes turning on my TV, PS5, and AVR easier and quicker. I enjoy the fact that I can use any remote to fix the volume so there is always a remote close when we need a quick mute or change in the volume.
I find the HEOS app to be a little clunky, but I am loving it anyway. I can run high-definition audio through streaming, which is a huge improvement from using Apple Airplay 2 or Bluetooth. It also lets me talk on the phone, send and receive messages, etc. without interrupting the music.
Right now, I am still tweaking my settings, but I can definitely say that the sound is really good. Have I heard better? Sure. This isn't an 11-channel receiver with Dirac, a 200 watt-per-channel, high-end "audiophile"-grade component, or a tube amp. It is best at multi-channel audio and does really well for music, especially with a good set of speakers and quality sub with parametric EQ.
My speakers have are low sensitivity (84dB), and the 2800H puts out enough grunt to listen give nuance and life to music in listening position, to bump the music to listen in my kitchen two rooms over, or watch at theater-level volume in my medium-sized living room with 8-foot ceilings. This thing is getting daily use, and it is more than enough to get the job done in style. For what I need, the 2800H is spot on.
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Reviewed in the United States on November 9, 2023