Custom jewelry, diamonds, gemstones and luxury watches, sourced and designed by a trusted GIA Diamond Graduate.
Custom engagement rings and one-of-a-kind pieces, natural and lab-grown diamonds, more than 7,000 loose gemstones, luxury watches, stone sourcing, and estate and consignment, with independent appraisals arranged through trusted third-party appraisers. By appointment on Long Island and in New York City, or online.
Every piece starts with the right stone.
We don't mass-produce. We source the diamond or gemstone, design around it with you, and work with many partners to bring your jewelry dreams to life.
Custom and Bridal Design
Engagement rings, wedding bands and anniversary pieces, from classic solitaires to fully original designs. We can also remake an old ring into something new. Build your ring online →
Custom engagement rings on Long Island →
Designer-Cut Gemstones
Tanzanite, tourmaline, sapphire, spinel, jadeite and more, including stones cut by AGTA Spectrum Award winners Mark Gronlund and Larry Woods.
Diamonds, Natural or Lab-Grown
GIA- and IGI-certified natural and lab-grown diamonds in VS quality and above. We explain the difference honestly so you can choose what's right for you.
World-class gemstones by Mark Gronlund
Mark Gronlund is a multi-time first-place AGTA Spectrum Award winner, and many of the stones we set come from his wheel: concave and starburst cuts that throw light in a way a standard cut can't. A few of his stones from our collection are pictured here.
See Gronlund-cut stones in the collection
From your idea to a piece that's yours alone.
- 1Share your ideaA link, photo or sketch, or meet with us in person or online.
- 2Get your quoteStone options and a detailed invoice, with applicable tax. Insured shipping is billed separately.
- 3Approve and place a deposit50% or more starts the work. Zelle preferred; card, wire or cash also accepted.
- 4Design and craftYou approve a detailed 3D design before anything is made.
- 5Approve and receiveUp to three weeks. Balance due when you approve the finished piece.
A client wanted an engagement ring with two emerald-eyed elephants cradling the center diamond. We took it from a sketch through CAD to a hand-forged ring in rose gold, delivered on schedule.
“He was able to complete the ring in the timeframe he promised and delivered me a perfect ring, for a perfect moment.”Sean K., Google review
“I can honestly say that the ring turned out even more beautiful than I imagined. I truly appreciate your craftsmanship, attention to detail, and dedication to making it exactly what I wanted. Thank you so much, Mark, for doing such an amazing job! I absolutely love my ring!”Maria O., the ring's owner · Google review, October 2026 · More reviews
Recent work
See the full collection →
What the same money buys.
About $5,000 each, round, VS1 clarity, top cut grade. Lab-grown diamonds are real diamonds, and we'll show you exactly how they compare with natural ones.
Shown to scale. Retailer figures: Blue Nile listings, September 2026. MM Fine figure: a 13.66ct IGI-graded lab-grown diamond from our current sourcing. Availability and pricing change daily.
Lab-grown or natural? Know the facts before you buy.
Lab-grown stones now make up most U.S. engagement rings, and their prices have fallen about 90% since 2018. Marc Merritt, a GIA-educated diamond grader, explains what that means for you.
Read the guideMore ways we help
Independent appraisals
Accurate valuations for jewelry and watches, working with respected appraisers including Deborah Villepigue, The Jewelry Appraiser.
Luxury watches
Brokerage of Rolex, Panerai, Omega and other fine timepieces with certified warranties, plus expert servicing.
Stone sourcing
Looking for a specific diamond or gemstone? We search our supplier network to find it for you.
Estate and consignment
New and estate jewelry at significantly discounted prices. Ask about our consigned pieces.
Recent timepieces we've brokered
We source and broker fine timepieces with certified warranties. Tell us the reference you're after and we'll find it.
Rolex Day-Date 4018kt Everose gold, chocolate diamond dial. A grail piece.
Rolex Cosmograph Daytona18kt Everose gold with black subdials.
Panerai Luminor GMT, PAM 531Black sandwich dial, Super-LumiNova. One of the many fine watch brands we source.
Omega Seamaster Professional 300M ChronographBlue wave dial, steel bracelet. Another of the fine watch brands we source.
Browse more than 7,000 loose gemstones
Sapphires, emeralds, rubies, tourmalines, tanzanite, aquamarine, garnet, topaz and more, with photos, sizes and pricing, available through our cutting partners and ready to be set into a piece designed around you.
Browse the gemstones Ask about a stoneReferral Program. Refer a friend and receive an Amazon gift card of up to $125 when they make a purchase. See how it works.
4.9 ★ · 32 Google reviews · GIA-educated grader · Est. 2018 Read all reviews → Leave a review
Unveiling the Secret to Engagement Ring Bliss
Marc's interactive guide to choosing and presenting an engagement ring: diamond quality and value, natural vs. lab-grown, GIA certification, settings, budgeting and proposal ideas.
Upcoming gem and mineral shows
Shows within a few hours of Long Island, updated monthly. See the full list and where to find us.
From the blog
Marc writes about famous diamonds, birthstones, gemology and how custom pieces are made. See all articles.
A lifelong gem collector who designs with you.
Marc's fascination with gemstones began at age ten, on a trip to the Grand Canyon. That first collection grew to more than 500 mineral specimens, now housed at a children's teaching museum in New Jersey.
A GIA Diamond Program Graduate with gemologist training in New York City, Marc holds an MBA and brings a banker's care for value and transparency to every piece. He founded MM Fine Jewelry and Gems Inc. in 2018 and owns it together with his wife, Marylene. They work with many partners to bring your jewelry dreams to life.
More about Marc: credentials, shows and video
Book a consultation
Tell us what you have in mind. We'll get back to you to set up a time: in person at a place that suits you on Long Island or in New York City, or online.
Book a video consultation → 30 minutes on Zoom, pick your own time. Or use the form for an in-person visit or a quote.