Custom fine jewelry, designed with you.
Engagement rings, one-of-a-kind pieces and designer-cut gemstones, crafted by a GIA Diamond Program Graduate. By appointment in Rockville Centre, New York, and online.
Marc and Marylene MerrittOwners, MM Fine Jewelry and Gems Inc.
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.
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. Watch a few of his pieces from our collection.
See Gronlund-cut stones in the collectionFrom your idea to a piece that's yours alone.
- 1ConsultationTell us your style, the stone you have in mind and your budget. In person or online.
- 2Stone selectionWe source options through our supplier network and walk you through each one.
- 3Sketch and CADYou see and approve a detailed 3D design before anything is made.
- 4Handcrafted and deliveredYour piece is made by hand, finished and delivered, with any fit adjustments after.
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
Recent work
See the full collection →
Burmese spinel pendant
Two exceptional Burmese spinels in a custom mount: a 6.7ct orange-red center of VVS1 clarity and a 5.6ct flawless purple-pink drop, framed by 0.68ct of VVS–VS, F–G diamonds. Both spinels are certified.
Fine spinel from Burma (Myanmar) is among the rarest gems in the world. For centuries it was mistaken for ruby; the famous “Black Prince’s Ruby” in the British Imperial State Crown is actually a spinel.
Inquire about this pieceSee it in motion
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.
More 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.
Two recent Rolex pieces we brokered
We source and broker fine timepieces with certified warranties. Tell us the reference you're after and we'll find it.
Some of the gemstones available now
Topaz, tourmaline, garnet, citrine, fire opal, peridot, amethyst, emerald and more, ready to be set into a piece designed around you. Ask us what's in stock or tell us what you're looking for.
Ask about a gemstoneReferral Program. Refer a friend and receive an Amazon gift card of up to $125 when they make a purchase. See how it works.
In our clients' words
“He showed me a variety of high quality beautiful stones before the watermelon tourmaline stole my heart.”
“He created a completely new design for an old ring I wanted to change into a newer design.”
“He took much time to educate me regarding my purchase.”
“Not enough can be said about the quality of his workmanship.”
“This jeweler's focus on educating clients highlights their transparency.”
“The precision, attention to detail and overall love and care are shown in his work.”
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.
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.
Book a consultation
Tell us what you have in mind. We'll get back to you to set up a time, in person in Rockville Centre or online.